expression, noun
caged bird
Literal meaning: a bird kept in a cage. Also used metaphorically for a person confined or lacking freedom.
籠の鳥は外の世界を知らない。
A caged bird does not know the outside world.
expression, noun
person whose freedom is restricted; kept woman
Idiomatic use referring to a person, especially a woman (prostitute, mistress, concubine), whose life is controlled and confined by someone else.
She lived a life just like a caged bird.
Compound of 籠 (かご, 'cage') + の (possessive particle) + 鳥 (とり, 'bird'). The idiomatic sense is a metaphorical extension of the literal meaning.