Rheum

Rheum ( /ˈruːm/; from Greek: ῥεῦμα, rheuma, a flowing, rheum) is thin mucus naturally discharged as a watery substance from the eyes, nose or mouth during sleep (contrast mucopurulent discharge). Rheum dries and gathers as a crust in the corners of the eyes or mouth, on the eyelids, or under the nose. It is formed by a combination of mucus (in the case of the eyes, consisting of mucin discharged from the cornea or conjunctiva), nasal mucus, blood cells, skin cells, or dust. Rheum from the eyes is particularly common and is in common usage called eye gunk, sleepydust, sleep, sleepys, sleepers, eye goop, eye crud, eye crust, eye bogeys, eye boogers, and others.