How does Google actually decide what counts as 'trending' right now?

Curious how Google Trends works under the hood — is it just raw search volume, or something more specific?

Google Trends' "Trending now" feature specifically looks for search queries experiencing a recent surge in interest relative to their normal volume, and it groups related queries into a single "trend" or cluster (for example, several variations of a person's name, or a name plus an event, might all roll up into one trending item) rather than listing every related search separately. The underlying data comes from an anonymized, aggregated sample of actual Google searches — Google doesn't process every single search for this in real time, but the sample is large enough (given billions of daily searches) to be representative. Trends refresh roughly every ten minutes, and each trend is marked "Active" if it's still being searched more than usual, or "Lasted" once it's fallen back to typical volume — though a trend that's ended can re-emerge and go active again if interest spikes a second time (which is common with ongoing news stories or multi-day events).