What goes in the album field?
The full studio album, mini-album, or best-of/compilation album on which the song appears. Singles should never go in the album field. If the song only appears on a single, not on any album, leave the album field blank. If the song is a B-side/coupling track and you would like to note the single on which it appears, you can put "c/w [single's leading track]" in the Description field.
The exception to this is the Vocaloid Original Songs category, in which the album field should be the name of the Vocaloid who "performs" the song (or Multiple Vocaloids if more than one).
Additionally, on a page for an anime or video game, the album field should only be for albums related to the show/game, such as soundtracks, vocal collections, or image albums. If a song appears on an album by its artist which is otherwise unrelated to the show/game, don't list that as its album on the show/game page.