Photographers Kevin Burg and Jamie Beck coined and popularized the term around 2011. Shot with a camera locked down on a tripod, a short clip gets masked so everything except one region freezes on a single still frame — steam off a coffee cup, one strand of hair, a flag — and only that region loops.
The seam between the frozen area and the moving one has to be invisible. Even a tiny bit of tripod shake creates a mismatch in jitter between the still background and the living region, and the composite gives itself away — which is why a rock-solid tripod is non-negotiable from the moment of the shoot.
It had a huge moment early on Instagram and is still used in ad banners and product pages today, precisely because it holds attention longer than a flat still image without being as distracting as full video.
When to use
Keep the moving region small — 5–10% of the frame at most. Make it too large and it just reads as a choppy, broken video.