Fetching details from the dictionary...
small bird (like a swallow or sparrow)
small-minded person; person lacking in character
燕雀安んぞ鴻鵠の志を知らんや。
How can a sparrow know the ambition of a swan?
庭先に燕雀が群れて餌を啄んでいた。
Small birds flocked in the garden, pecking at food.
大志を抱く者を燕雀には理解できない。
Those with petty minds cannot understand the ambitious.