the ability to form pictures in the mind:
vivid imagination My younger son has a very vivid (= active) imagination.
I can never make up stories - I have absolutely no imagination.
capture/catch the imagination of For some reason the story captured/caught the imagination of the public (= made them very interested).
by any stretch of the imagination It couldn't by any stretch of the imagination be described as a (= it is certainly not a) beautiful city.
leave nothing to the imagination There's a sex scene in the film which apparently leaves nothing to the imagination (= shows sexual parts of the body very clearly).
something that you think exists or is true, although in fact it is not real or true:
Was she paying him a lot of attention or was it just my imagination?
Is it my imagination or is David behaving strangely at the moment?
the ability to think of new ideas:
It's a job that needs someone with a bit of imagination.