the.com/mucus

means The slick, slippery fluid your mucous membranes produce to trap particles, keep tissues moist, and stop you drying out or getting invaded from the inside.

from From Latin mucus, meaning 'slime' or 'nasal mucus,' itself related to the Latin verb emungere, 'to blow the nose' or 'wipe clean.' That Latin root connects further back to a Proto-Indo-European base associated with 'slippery' or 'slimy,' which also gave English the word 'mucilage.' So the word has meant exactly this gunk, in roughly this sense, for over two thousand years — a rare case of etymology being almost disappointingly literal.