Watch time is the total minutes and hours people spent watching your content. Views count how many times a video started; watch time counts how much attention it actually held. Platforms treat it as their honest currency.
A feed's business is deciding where attention goes, so it optimises for the metric measured IN attention.
Two videos with the same view count can differ ten times over in watch time. The ranking treats them completely differently: the one that held people gets recommended again; the one people abandoned stops being offered. Session time stacks on top: platforms also credit content that keeps people on the app afterwards.
Longer videos are the efficient vehicle, but only after retention is fixed: length multiplies whatever hold you have, good or bad.
Series and playlists chain videos into sessions. Strong openings protect the multiplier. And on YouTube, all of it accumulates toward the Partner Programme's meter, which is why watch time is the metric that most directly becomes money.
Watch time is the general metric on every platform. Watch hours are YouTube's accumulated total, the one counted for monetisation. Same idea, different scoreboard.
They build their own short-form watch metrics. On YouTube specifically, Shorts watch time does NOT count toward the 4,000 watch hours gate; it has its own views-based route.
YouTube Studio reports it directly. TikTok and Instagram report average watch time and completion per video, which multiply out to the same thing.
Every definition lives in the full glossary, and the services behind the vocabulary are on the services page.