Glossary
What is Class B airspace?
The controlled airspace surrounding the nation's busiest airports, built in tiers that are often described as an upside-down wedding cake. Entry needs a specific clearance: hearing your call sign is not enough, because the controller has to say you are cleared into the Class B.
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.