Glossary
What is Class E airspace?
Controlled airspace that is not Class A, B, C or D. It fills most of the country above a published floor and reaches down to the surface at many airports with instrument approaches. Flying in it under VFR needs no clearance and no radio call, but the cloud and visibility minimums are tighter than in uncontrolled airspace.
That is the whole entry for now. The longer version, with the mechanics and worked examples, is still to be written. See autorotation for how those read once they exist.