The ED is an anime's ending sequence: the closing song and credit montage, usually about ninety seconds, that ends most episodes. It is numbered when a series changes it (ED 1, ED 2, and so on).
Where the OP is the front door, the ED is the room you sit in afterwards. Ending sequences often carry a series' emotional register: reflective, playful, elegiac, or quietly comic, and staff use them to show characters in moods the episode itself had no time for. A tonal shift in the ED mid-run is one of anime's reliable signals that a story has darkened.
EDs also run a practical errand. Credits roll there, and the next-episode preview traditionally follows, which made the ED block the part of a broadcast a committed viewer never skipped. Streaming moved previews around and added skip buttons, and the ED became the most-skipped ninety seconds in the medium, which fans of great endings lament on schedule.
Songs matter here too, and ED themes are often the softer, more beloved half of a soundtrack. On this site, OP and ED are treated as first-class facts of a series: titles, performers, and which episodes a sequence covers are all standard knowledge for a subject's fans. A small number of series build their final episode's ED into the story itself, letting the closing sequence play over the last scene, a device reserved for endings the staff want to land softly.
In use"The ED changed to a slower song after the midpoint of the run, and the credits scenes changed with it."