Flight Modes are combinations of different model set ups that enhance control under widely different conditions for a given model.  For example glider pilots may want one set of control responses for launch, another for riding a thermal or for descending, and yet another for landing.  Flight modes allow changing set ups with the flip of a switch.  OpenTx on the Taranis provides up to seven flight modes:

FM0 – default flight mode can be named. Speed parameters are provided for smooth transitions to other flight modes.

FM1 – FM7 – seven flight modes can be named and assigned to unique switch positions. Speed parameters are provided for smooth transitions.