What is Middle?

Middle definition and meaning on Dictionary terms:

equally distant from the extremes or outer limits; central: the middle point of a line; the middle singer in a trio.
intermediate or intervening: the middle distance.
medium or average: a man of middle size.
(initial capital letter) (in the history of a language) intermediate between periods classified as Old and New or Modern: Middle English.
Grammar. (in some languages) noting a voice of verb inflection in which the subject is represented as acting on or for itself, in contrast to the active voice in which the subject acts, and the passive voice in which the subject is acted upon, as in Greek, egrapsam?n