noun
eye discharge; sleep; eye mucus
Refers to the crusty or sticky substance that forms in the corners of the eyes, especially after sleeping. A common, everyday word.
朝起きたら目くそがついていた。
When I woke up in the morning, I had sleep in my eyes.
目くそを取ってから顔を洗った。
I removed the eye discharge and then washed my face.
Also means eye discharge; 目やに is slightly more formal or medical-sounding, while 目くそ is more colloquial and everyday.
Compound of 目 (eye) and くそ (excrement/waste matter), literally 'eye waste'. The word is native Japanese and its origin is straightforward.