What does slithy mean?

Jabberwocky is a nonsense poem, most of what you read seems to make a story, but a large number of the Words are not real. In the case of Slithy Toves, there is no such thing, but as you read the poem, they are clearly capable of gyring and gimbling. In my imagination they are toad like creatures moving in a swamp, but you could equally imagine flowers waving in the breeze. What they are is not important.