Lubricant

A lubricant is any product whose job is to reduce friction: an oil, a grease, or a specialty compound. This category uses the singular name. The posts that review a named grease are filed so a reader can tell a lubricant from a kitchen fat.

Lubricating grease is thick. Lubricating oil is liquid. Used cooking oil is a kitchen waste, not a lubricant, even though both are oily. Trap grease is not a lubricant either. The words share a texture and not a use.