TDM or Time Division Multiplexing is a method to share the channel and transmit data. The channel is broken down into fixed-sized slots and distributes those slots among the various inputs that need to be sent out. You rotate the time slots among the inputs, by switching from one to another. For example, if you have A, B, C, D as input to TDM logic, A is sent first then B, C and D, in the time slots we have DCBA as a packet of data sitting next to each other.