Slime was a substance known on many planets as existing both naturally and artificially. It was also known to either be secreted by, or lived in, by several animal species; among them the Mellanoid slime worm and Denebian slime devil. (TOS: "The Trouble with Tribbles"; TNG: "Coming of Age")
Slime may be referred to in the vernacular as "goo". (TNG: "All Good Things...")
A similar substance to slime was sludge.