what is m coach in train

M1 coach is an AC three-tier economy class coach in Indian Railways. It is one of the coaches that come under the AC three-tier economy class, which is denoted by M1, M2, M3, and so on. The M in M1 stands for AC three-tier economy coach, and the number 1 stands for first. The AC three-tier economy class coaches are modernized air-conditioned coaches with sleeping berths. The berths are usually arranged as in 3A, with two tiers across the width and three lengthwise. The appointments are similar to 3A, and bedding is included.