Hairball means: Hairball is a clump of hair. Sometimes hairballs can block the digestive system. Also known as ‘trichobezoar.
(in Medical Dictionary)

What else does Hairball mean?

Small amounts of hair that accumulate in an animal’s stomach, intestine, or stomach, like a cat. This happens when it licks its hair and swallows the hair.
(in Merlin Dictionary)