An imaginary place conceived of as being visible in the image shown in a looking-glass, especially one in which the principles which underpin the real world (as the rules of logic, the laws of physics, etc.) operate differently, or in reverse; also in extended use.
Chiefly with reference or allusion to the imaginary world depicted in ‘L. Carroll’ Through the Looking-glass (1871).
Late 19th century; earliest use found in ‘Lewis Carroll’ (1832–1898), author, mathematician, and photographer (real name Charles Lutwidge Dodgson).