Dwell time is the amount of time someone spends with your content — how long they linger on a post, read a caption, or watch a video before scrolling away. For video it shows up as average watch time and completion rate; for static posts and carousels it is the seconds of attention a piece holds.
It matters because attention is the currency ranking systems trust most. A post people actually stop for and finish tells the algorithm the content is worth showing to more people, so dwell time and completion often predict reach better than likes do.
Lengthen it with a hook that creates an open loop, pacing that keeps a reason to keep watching or swiping, captions and on-screen text for sound-off viewing, and carousels that reward the next swipe. Watch where viewers drop off and fix that exact moment.