Following are various types of seats which can be reserved in Indian Railways trains.
2S - Second Sitting
These seats are non-air conditioned. Generally day running trains have this class of reservation.
SL - Sleeper Class
This class is the most popular in Indian Railays. Most of the express train have SL class. This is non-air conditioned class. From 9pm to 6am you can sleep on the berth. During the day lower berths are used for sitting.
CC - Chair Car
3+2 arragement. AC Coach.
EC - Executive chair car
First AC Chair car or Executive Chair car . 2+2 arrangement, more spacious designed especially for business class
EA - Anubhuthi chair car
The Anubhuti coaches are attached in Shatabdi trains as additional executive class and have ergonomically designed seats.
3A - AC three tier
3 beds - Upper , Middle and Lower Beds. AC coach.
2A - AC two tier
2 beds - Upper and Lower beds. AC coach. These seats have higher head room as compared to 3AC seats.
1A - AC first class
Most expensive AC seats, lockable cabin of 2 beds and 4 beds configuration are available for booking. Seat numbers are only alloted after charting.