What is FTSW on an amp?

FTSW is an input for a foot-switch, a device you can use to quickly change presets while playing. Some amp manufacturers like for example Fender use them, however in my opinion there is no point in buying a foot-switch, simply buy a desired effect and you can tap it on and off with your foot too, plus the quality of the effect is going to be much better than the quality of the effect in an amp.