What is meant by "second sitting" on Indian Railways?

"Second sitting" is the cheapest ticket that can be reserved on a railway. It has wooden bench seating and no air conditioning. Additionally, the ticket holder is not guaranteed a seat.

These sections of the train can be overcrowded at high-travel times. One level up is the AC chair car, which has nicer seats and air conditioning. Second sitting is generally only for day travel, although it can be booked at night, too. For nighttime travel, however, berths can be rented, which are private compartments generally for two to four people. Some berths are completely isolated while others are open to the train. Nighttime travel also comes with both air-conditioned and non-air-conditioned options.