A highlight medley is a preview video that an act or its label posts in the run-up to a release. Instead of a single trailer built around one song, it strings together short excerpts from every track on the upcoming project, usually in the same order the tracklist will follow.
The whole video usually runs a couple of minutes, which means each track only gets a short snippet, often just enough to catch a melody, a beat switch, or a few seconds of a chorus before the video cuts to the next song on the list.
As each snippet plays, the track title is typically shown on screen. Because full tracklists are not always announced in advance, this is often the first moment fans can see, in order, exactly what songs are on the release.
These videos are posted on the act's or label's official channel, usually with a description that repeats the release date and a pre-order link. Fans will also come across related formats around the same time, such as a track sampler that gives one clip per song across a series, or a showcase, which is a live event tied to the release.