Sound of movement
A whoosh is the sound of something passing quickly: air moved by a swinging object, or a burst of filtered noise that rises and falls. In music it fills the moment before a section changes; in video it sells a cut or a title. Most are under two seconds long and peak in the middle.
Choosing and placing
Time the loudest point of the whoosh to land exactly on the cut or downbeat, not its start. For music, a high-pass keeps it out of the bass, and a tempo-synced delay can stretch it into a transition. Recorded whooshes (sticks, cloth, ropes swung past a microphone) sound natural; synthesised noise sweeps sound cleaner and more electronic.
Free sound effect libraries are full of whooshes, with licences from CC0 to non-commercial. Turn on Commercial-safe to keep only the ones you can publish.