OFDM : Orthogonal Frequency Division Multiplexing
It is a modulation method that divides a channel into multiple narrow orthogonal bands that are spaced so they don’t interfere with one another. Each band is divided into hundreds or even thousands of 15-kHz wide subcarriers.
FDMA: Frequency Division Multiple Access
Here a channel/band is divided into multiple sub bands & each is used by single user.
TDMA : Time Division Multiple Access
Here a single band/channel multiple time slots.