This page forms part of an etymology course that gives an outline of the development of English. It is written in a sequence that you may want to follow. The best place to start, if you want to follow the whole course, is Etymology course, or, if you are only interested in English, Development of English. You may also arrive at any of these articles from other links. For more information about the history of English, you should of course read a good history of the language, such as Baugh (1993), Strang (1970), or Crystal (2005)
Middle English is an historical term used in the study of the English language. It refers to the forms of English being used between roughly 1100 and 1500. Before the Norman Conquest, the language of England was Old English; from the accession of the Tudors in 1485, we can see Modern English. In between - logically enough - there was Middle English.