Here’s one definition of conceit.

An intellectually ingenious poetic comparison or image, such as an analogy or metaphor. (source)

The difference between conceit and the other comparisons is the dramatic nature of it. The comparison is unconventional, unlikely, not obvious. You have to use your imagination to see the connection.

Examples are: “My life is like an online game” and “A broken heart is like a damaged clock.” (source)