Actually, it's food particles that become trapped in the pockets of your tonsils. My pediatrician calls it "petrified", meaning that there is no infection, just a lot of that stuff lingering within the tonsil.
My son has very enlarged tonsils with that stuff and had strep throat on and off since he was a baby until he got to be about 10.
Doctors advice was to gargle with salt water as that is an astringent that can help to shrink the tonsils and also help cleanse that stuff out of there.
I have it, myself, to an extent but it's nothing to worry about...just might give you a bit of bad breath so keep the breathmints handy!