EMS stands for electrical muscle stimulation. The full-body version people train in is called WB-EMS (whole-body EMS).

The plain version: you wear a snug suit lined with electrode pads that sit over your major muscle groups — chest, back, abs, glutes, thighs, arms. A control unit sends gentle electrical impulses through those pads, and the muscles contract on their own. You do light, controlled movements (squats, presses, holds) while the impulses fire, so your muscles work from the inside (the impulse) and the outside (the movement) at the same time.

A typical session is about 20 minutes, once or twice a week. The appeal is time-efficiency — you recruit a lot of muscle in a short window. The evidence is strongest for building strength and muscle; it is not a reliable fat-loss shortcut on its own. If you're brand new, read the pinned safety notice in the Safety board before your first session.