WSJT is the name of a computer program and stands for "Weak Signal communication by K1JT. The program supports two communication modes, known as FSK441 and JT44.

FSK441 is designed for MS (Meteor Scatter) communication using brief "pings" of signals reflected from the ionized trails of meteors.

JT44 is designed for communtication with very weak signals of roughly constant signal strength. It's ideal for tropo scatter and EME (Earth-Moon-Earth) communications.