OFDMA stands for Orthogonal Frequency Division Multiple Access. This channel access method has been available since WiFi 6 (link) and has a double advantage:
On the one hand, a channel can be divided into even more sub-channels than before. Alternatively, the distribution of one or more subchannels can be assigned to one or more clients.
If a client uses little bandwidth, the remaining bandwidth can be used for other clients. Only WiFi 6 has this channel access method.