Multiple Access it is a combination of OFDMA (orthogonal frequency-division multiple access), TDMA (Time-division multiple access), and SDMA (Space Division Multiple Access).
OFDMA is based on Orthogonal Frequency Division Multiplexing (OFDM) with a cyclic prefix (CP); the transmission to/from different UEs uses mutually orthogonal frequency assignments. With granularity in frequency domain assignment equal to one resource block consisting of 12 subcarriers as illustrated by this grid.
TDMA is based on the transmission to/from different UEs with separation in time. The granularity in the time domain is equal one slot consisting of 14 OFDM symbols, or 2, 4, 7 OFDM symbols within one mini-slot. The physical length of one slot ranges from 0.125ms to 1ms depending on the sub-carrier spacing.
The SDMA , also known as multi-user MIMO, is referring to the possibility to transmit to/from multiple users using the same time-frequency resource as part of the advanced-antenna capabilities.