There are three meanings of Sanskaar in Hindu Religion.
(1) Perfecting - Whatever basic habits are formed in very childhood are also called Sanskaar in later years, e.g. "If parents keep the foundation of good Sanskaar in a child, he will become a good man in later years." For example if Parents makes a habit to do daily chores (a set of daily routine) in early morning time, say at 5.00 am, and if it continues till death, that is called Sanskaar. Such habits die hard, sometimes do not die at all.

(2) Whatever actions we have done in our previous lives, they form our future and nature in our next lives; because only according to them our next life is decided. This nature results from such actions is called Sanskaar. When a person behaves in a certain way without teaching it, then it is said that "his Sanskaar are like that".

(3) Purifying. Purifying of a person is done by ceremonies. Ceremonies for sanctifying. According to Paraashar there are 13 Sanskaar; according to Manu Smriti there are 12 Sanskaar, and according to Aashwalaayan there are 11 such ceremonies, among which some of which have become obsolete. There are only 6 ceremonies which still are performed by most people. Although there are 48 Sanskaar (see below) in all, but 16 Sanskaar are principal Sanskaar or say religious rites of a person since his birth till death at time to time, such as -

(1) Conception (Garbhaadhaan) Sanskaar (as soon as the conception is known) 
(2) Punsavan (Milk) (performed in 3rd month)
(3) Vedic Rites (Seemantnayan - performed in 6th month)
--(4) Janm or Jaatkarm Sanskaar (at the time of birth)
--(5) Naamkarn Sanskaar (Nishkraman - after some time of birth - shown to Soorya),
--(6) Nishkraman Sanskaar - Taking the child outdoors first time.
--(7) Annpraashan Sanskaar (When a child is given cooked grains for the first time)
--(8) Mundan (Choodaakaran) Sanskaar - in this all first hair (hair of birth) of head are shaved.
--(9) Karn Chhedan Sanskaar - In this the child's ear are pierced. It is done normally in the 3rd or 5th years of age.
--(10) Yagyopaveet or Upanayan Sanskaar (in which Yagyopaveet or Sacred Thread is given to child and he is sent to Guru) - see also  Upanayan
(11) Vedaarambh or Study of Ved (sometimes the 10th and 11th Samskaar are done together and sometimes at some interval)
--(12) Samaavartan Sanskaar - Completing the education. Although now-a-days education is never complete but it is performed when a basic education is completed.
--(13) Vivaah Sanskaar (marriage ceremony)
(14) Sarv Sanskaar - Preparing for Renunciation.
(15) Sanyaas (Avasthaa Dhyaan) - Renouncing.
--(16) Daah Sanskaar (Antyeshti) - last rites.

These Sanskaar are described in detail in Grihya Sootra (see also Sootra). A brief description of each of them is given on next page. The Sanskaar which have two dashes (--) before them are now-a-days the main Sanskaar in use; others are optional - (1) Janm Sanskaar, (2) Naamkarn Sanskaar, (3) Annapraashan Sanskaar, (4) Mundan Sanskaar, (5) Upanayan Sanskaar, (6) Vivaah Sanskaar, and (7) Daah Sanskaar. Others are optional.

Names of 48 Sanskaar
1. Gabhaadhaan
2. Punsavan
3. Seemaant Unnanam
4. Jaat Karm
5. Naam Karn
6. Anna Praashan
7. Choolam
8. Upanayan

9-12. Four Prajaapatya Ved Vrat performed in Gurukul

13. Samvartan Vrat on return from Gurukul

14-18 - Panch Yagya
14. Brahm Yagya
15. Dev Yagya
16. Pitri Yagya
17. Manushya Yagya - Atithi Yagya
18. Bhoot Yagya - Vaishwadev Yagya

19. Marriage (Paani Grahan)

20-27 - Seven Paak Yagya
20. Ashtak
21. Sthaalee Paak
22. Paarvan
23. Shraavanee
24. Aagraahyanee
25. Chaitree
26. Asaujee

27- 33 - Seven Havir Yagya (Hom Yagya)
27. Agni Aadhanaa
28. Agnihotra
29. Darshpaurn Maas
30. Aagraayan
31. Chaatur Maasya
32. Nirood Pashu Band
33. Sautraamani

34-40 - Seven Som Yagya
34. Agnishtom
35. Atyaagnishtom
36. Uktya
37. Shdashee
38. Vaajapeya
39. Atiraatra
40. Aptoryamaa