Microwave/Talk

How are microwaves defined? I see possibilites:

• The characteristic frequency of the molecules of solids and liquids
• Arbitrarily by wavelength
• The spectrum released by some specific source

Anybody know enough about the history to clarify this? The reason I ask is because I know that X and gamma rays overlap because they're classified by what emits them (high energy electrons and nuclear interactions, respectively). It also occurs to me that microwaves are used in radio communication and radar detection systems.--BlackGriffen