I agree with everyone else it's a hair ball and they are gross.
Regular brushing is a good routine to get into which we try at our house with pretty good success. I also use Cat Lax that I get from the vet. If I'm not sure "who did it" they all get a little strip of lax. Normally it's Thumper who is my barfer and I usually hear her gaging. Eleanor sounds like a seal screaming when she has hairball. First time I heard it I jumped a mile. Such a loud noise coming out of a little girl.