Dharm is so called because it holds, Dharm alone holds the people. Dharm word has been derived from the root Dhr - to hold and its etymological meaning is that which holds the world, or the people of the world, or the whole creation from microcosm to macrocosm. The Earth is also Dharatee because its origin is also from the root Dhr, because she holds all of us.

According to Bheeshm Pitaamaha, Dharm is, "Dhriti (Dhairya), Kshamaa, Dam, Asteya (not stealing), Shauch (cleanliness), Indriya-nigraha (control on senses), Dhee (intellect), Vidyaa, Satya, A-Krodh (not being angry)". Rishi also did not preach Dharm as Hinduism or Vaidik or Sanaatan Dharm. We added these adjectives to distinguish us from "Others". Rishi preached Dharm in the above sense and duties in elation to Varn and Aashram. The Buddha and Mahaaveer also preached Dharm, nor Buddhist or Jain religions.

Otherwise Dharm may mean any one, or more than one, or all of the following -
(1) Religious conduct - relationship between a person and God,
(2) Varnaashram Dharm - Duties according to one's Varn and Aashram
(3) Jaati Dharm - Duties because of being born in a particular species. Prescribed code of conduct, or nature - such as a scorpion's Dharm is to sting, or lion's Dharm is to eat other animals,
(4) Samaaj Dram - Duties toward people in the society
(5) Swabhaav Dharm - Particular natural characteristics
(6) Shraut Dharm - Duties toward God,
(7) Vaidik Dharm - The rules of conduct approved by God (God means Shaastra or Ved etc)
(8) Nyaaya Dharm - Justice,
(9) Prakriti Dharm - Laws of nature, such as all planets revolve around
(10) Aachaar Dharm
(11) Neeti Dharm
(12) Pravritti Dharm
(13) Nivritti Dharm

Dharm is those Karm which are prescribed for a person according to his Varn and Aashram. Dharm stands on four legs - Vidyaa (knowledge), Daan (donation), Tap (austerity), and Satya (truth). In Sat Yug Dharm's all legs are present; in Tretaa Yug it stands with three legs; in Dwaapar Yug, it stands with two legs and in Kali Yug it stands only with one leg - Daan.

If one has to translate the word Dharm, there is nothing better than the word "Value System".

There is only one true Dharm whose essential features were best described by Bheeshm Pitaamaha :
Dhriti, Kshamaa, Dam, Asteya, Shauch, Indriya-nigraha, Dhee, Vidyaa, Satyam, Akrodh : Dashakam Dharm Lakshanam.

This list excludes worship of deities, Yagya, Sanyaas or Karm, etc. In fact these are the MEANS to attain Dharm or Moksh, and the former are actual ingredients of Dharm itself. All other religions are man-made and divide humanity. Sanaatan Dharm is all embracing and tolerant. It has scope even for atheists. But it has no scope for the intolerant, because Dhriti is its first and foremost feature. Dharm and Dhriti are derived from the same root Dhr. A father may be Vaishnav, mother may be Shaakt, daughter may be Shaiv, and son may be atheist, yet all may live together with full harmony. Love and harmony is not broken even if the Vaishnav husband does not take food cooked by his Shaakt wife. Other cultures do not exhibit such toleration. But some modern persons now do not tolerate others at all.

According to Manu there are 10 characteristics of Dharm - (1) Dhriti (patience); (2) Kshamaa (forgiveness); (3) Dam (controlling one's mind); (4) A-Steya (not stealing); (5) Shauch (cleanliness); (6) Indriya Nigraha (controlling Indiyaan); (7) Saatwik Buddhi (good intellect); (8) Adhyaatm Vidyaa (spiritual knowledge) (9) Satya (Truth); and (10) A-Krodh (politeness).
[Naarad Puraan, p 651] [Agni Puraan, p 335]

[ Bhavishya Puraan, p 205] says that there are 10 means to earn Dharm - (1) Ahinsaa (non-violence), (2) Kshamaa (forgiveness), (3) Satya (Truth), (4) Namrataa (polity). (5) Shraddhaa (devotion), (6) Control on Indriya, (7) Daan (charity, donation, alms), (8) Yagya (Havan, Hom), (9) Tap (penance), and (10) Dhyaan (meditation).

Manu Smriti, 1/86, says that Tap, Gyaan, Yagya and Daan are the four feet of Dharm. In Sat Yug Dharm stands with his four feet. In Tretaa Yug he stands with three feet. In Dwaapar Yug he stands with two feet. In Kali Yug he stands with only one foot - Daan.

Dharm's one leg is of 432,000 years. (Kali Yug is 432,000 years - so one can understand that why Sat Yug is four times longer than Kali Yug - because in Sat Yug, Dharm stands with four feet.)
[Bhavishya Puraan, p 372]

Dharm is said to be of two types - Isht Dharm and Poort Dharm. Doing Yagya etc is called Isht Dharm, and digging wells, ponds etc is called Poort Dharm.
(Bhavishya Puraan, p 21)

King Shataaneek said - "Muni, Now I wish to know about five types of Smriti etc Dharm." Sumantu Muni said - "Hey Raajan, Now you listen to those five types of Dharm which Soorya told his Saarathee Arun. Soorya said - "Hey Garud, Smriti Dharm's root is Ved. Remembering the previously earned Gyaan is called Smriti. Smriti Dharm is of five types. By following these Dharm one attains Swarg and Moksh. First is Ved Dharm, second is Aashram Dharm, third is Varn Aashram Dharm, fourth is Gun Dharm, and the fifth is Naimittik Dharm. Following one's Dharm according to Varn and Aashram is called Varn Aashram and Aashram Dharm. Whichever Dharm is according to Gun (Sat, Raj, and Tam), it is called Gun Dharm. Whichever Dharm is according to a Nimitt (purpose), it is called Naimittik Dharm. This Dharm is based on Jaati (caste), money, and Gun (the three attributes - Sat, Raj and Tam).
[Bhavishya Puraan, p 197]

(1) Dharm literally means "that which is the support [of the human society] - a complete religious system of duty, ethics, theology and metaphysics. 
(2) Intrinsic propensity or nature of a living being or thing, for example the Dharm of fish is to swim, and of gold is to shine. 
(3) Statute, ordinance, law or moral law. The books of law are called Dharm Shaastra.
(4) Customary observance or practices, such as to serve our elders is our Dharm.
[Aangiras, p 188-189]

Dharm is eternal. The tradition views to see eternality is in two ways :
(a) permanent, fixed, not born, not grown, not modified, fixed, etc. (this is called Kootasth Nityat)
(b) flowing within two perspective of time and space (Pravaah Nitya).
--Kaal 'Time' is eternal (Kootasth Nitya)
--Temporal Time (history) is Pravaah Nitya.

The Pravaah Nitya Dharm is always viewed in the Conduct of individuals or groups. When the Pravaah Nitya Dharm of an organized society is joined with injunctions of Vidhi and Nishedh (see Vidhi-Nishedh) it is called religion in modern day societies.

What is Vidhi-Nishedh? It is: do's and don'ts with consequences. That is :
"do this or do not do this; do this so that you will attain merit (Punya); and
do not do this because if you do this you will earn demerits (Paap).

When Dharm becomes religion, Sanskaar become rituals - there a vast difference between Sanskaar and rituals. To know all this one should read Naasadeeya Sookt, and Sookt related to Srishti and Purush Sookt. For understanding the Pravaah Nitya Dharm more clearly, one should study the story of Kaushik Braahman in the Mahaabhaarat. It is a major source for understanding of the Pravaah Nitya Dharm.

Dharm has been defined by Mahaperiyaaval, the Kaanchee sage Shree Chandrasekharendra Saraswati Swamigal , as follows:
"Dharm is the root of the tree, Bhakti its flowers and Gyaanam its fruits "
The meaning of this statement is -
1. No flower or fruits are possible without roots.
2. We need to water the plant at its roots to grow and become a tree;
3. Unless the roots of a tree are tendered no flower and no fruits are possible.

Action at the roots and see the action at flower or fruit, therefore, Dharm is the core of all our actions, the joy of discharging ones Dharm (duties) which in turn binds one to one's Dharm and reciprocal is Bhakti. The fruit when Bhakti matures into oneness is Gyaan. This is the reason all Sanaatan Dharm Aachaarya, irrespective of the philosophy they vouch, advise their devotees to follow Dharm first and the rest will follow. Will any one water fruit or flower for the tree to grow? Likewise it is futile when one says he cannot observe Dharm but is a Bhakt or is a Gyaanee and there is no need for Dharm. The fact is that it is the other way round, when one attains Gyaan all things including Dharm detaches by its own accord no need to do anything to detach oneself.

However much one understands by intelligence learn and research worldly things and try to fit in God within the parameter of ones intellect is bound to fail; for God is beyond the ken of intellect knowing. Intellect functions in the tri states of Jaagrat, Swapn and Sushupti; when Manas stops all inner activities are stopped that is when the Self or Aatmaa or God shines by Itself leading to the fourth stage (fourth in comparison to the tri-states otherwise fourth is the only state in reality, the tri-states don't exist simply and until such time one experiences Tureeya one has to talk with ref to tri-states and hence the word "four") the state of Tureeya which is experiential. When this state is known, all other things are said to be known, for there is nothing other than this ONE state.

Dharm is, therefore, the first step and without the first step there is no second step let alone the last step.

About Dharm
It is said about Dharm that
--"Sukhasya Moolam Dharm:" (Yog Vashishth) - means Dharm is the root of Sukh (happiness).
--"Dharm Aiv Hato Hanti | Dharmo Rakshati Rakshit:" - means the one not observing Dharm is destroyed while the one following it meticulously is protected by Dharm itself
--Swalpam Api Asya Dharmasya Traayato Mahato Bhayaat - (Geetaa, 2-40) - means following Dharm even to a small extent protects one from great danger.

Even if one's own Dharm (according to one's own Varn and Aashram) is without Punya or merits, still it is good for the man; but other's Dharm is fearful in spite of being full of merit. Dharm is not to be adopted by oneself; but to lead a good life, free from evils, vices and wrong paths is the truest form of one's religion.