Sliminess is a surprisingly important character for identification. Of course, this means that there are many terms for different degrees of sliminess, not all of the (in my humble opinion) meaningful.
In this database, the following terms are used:
Slimy, meaning a definite layer of slime on top of the cap.
Tacky, meaning the surface is somewhat sticky, but not really, and it's certainly not got slimy stuff on it. A leaf might stick to your fingers if they were tacky, but nothing heavier. A post-it note is about this level of stickiness.
Viscid, an in-between condition where the cap is clearly sticky or slimy, but you can't distinguish a separate layer of "stuff" on top of it that's making it so. I consider subviscid a synonym for tacky.
Viscidcaps often dehydrate and lose their stickiness as the mushroom grows, but will rehydrate and become sticky again if you wet the pileus surface.
One frequently needs to detect a viscidmushroom that is no longer sticky. You can usually tell because it will have bits of leaves and other stuff stuck to it, back from the time when it came up through the soil and still was sticky. This debris gets sort of cemented to the cap surface as it dries out.
Also, a once-slimy/viscid surface is often shiny, since slimy tends to dry that way.