The minor modes determine whether or not certain actions take place. For example, when abbrev mode is on, abbrevs are automatically expanded when typed into a buffer. Buffers may possess any number of minor modes.

an optional feature of Emacs that can be switched on or off independently of other modes in operation

a set of customization options or functions that makes Emacs behave in a certain way

One of two colorings, generally dark and unstable, applied to a key, characterized by the minor scale and the resulting predominance of minor triads.

a key based on the minor scale