A past participle used in the passive voice as an adjective to describe an actor or actress who will always be known for one role he/she played early in his/her career. More than just typecast, the performer is known for one specific role.
Origin is Curtis Armstrong's character Booger in REVENGE OF THE NERDS. People don't remember Armstrong's realname -- they only know him as "Booger."
Vaguely related to stereotyping.
"Hey, look! There's Frodo! He's been totally boogered." -- what to say when Elijah Wood walks by.