1.Definition: being neither at the beginning nor at the end in a series
"The middle point on a line"
2.Definition: between an earlier and a later period of time
"In the middle years", "In his middle thirties"
4.Definition: of a stage in the development of a language or literature between earlier and later stages
"Middle English is the English language from about 1100 to 1500", "Middle Gaelic"