An inapt phrase, statement, or comparison is not the right one for that situation — it does not fit. We use this adjective mostly about language: an inapt remark, an inapt description, an inapt example. It is fairly formal and a little old-fashioned; many people would just say “not quite the right word” or “a poor fit.” Though actually, do not mix it up with inept. Inept is about a person being clumsy or unskilled. Inapt is about a choice, usually of words, that misses the mark. A clever speaker can still pick an inapt example. The warm opposite is apt: an apt phrase is exactly the right one.