For definitions' sake:

(I'm assuming you know what midi is).

Midi styles are groupings of midi instruments that generate arrangements according to the chords you enter (as well as other info you supply, like key, tempo, certain rhythmical elements, etc.) in a particular style/genre/feel.

REAL tracks and REAL drums are actual recordings of actual musicians playing actual instruments. Not sampled instruments...real playing by top-drawer studio musicians. These tracks are arranged in a bunch of Styles that work well together to form a "band", or you can combine them in other ways to make your own "band". The chords (and other info you provide) call up segments of much longer recordings and have those recordings follow your chords, tempo, key, and other elements. That's the short version.

BIAB 2021 Audiophile. Windows 10 64bit. Songwriter, lyricist, composer(?) loving all styles. Some pre-BIAB music from Farfetched Tangmo Band's first CD. https://alonetone.com/tangmo/playlists/close-to-the-ground