Slo-mo is short for slow motion: action that is shown happening more slowly than it did in real life, so you can see each bit of it. Films use slo-mo for a jump, a punch, an explosion, a look on someone’s face. Sports replays put a goal or a photo finish in slo-mo so the crowd can judge it. Video games use it as a trick: time slows, and you line up a shot. People say it as a noun (watch it in slo-mo), as a kind of adjective (a slo-mo replay), and sometimes as a verb (they slo-mo’d the catch). It is informal and belongs to screens — cinema, television, phones, games — not to a clock running slowly in the real world. If a person walks slowly down a corridor, that is not slo-mo unless you are joking that it looks like a film. The spelling tells you it is clipped speech: slo for slow, mo for motion, usually with a hyphen. You will also see slo mo and slomo. In a formal essay, slow motion is the full form; in a chat about a clip, slo-mo is what people type. Though actually, the effect is often fake in the sense that the camera filmed at a high frame rate and we play it back slowly — the event itself was fast. Learners only need the idea: the picture has been stretched in time so we can watch it.