A legendary individual, who will stop at nothing to get his/her way. Usually used in the context of pursuing members of he opposite sex, drinking vast amonts of alcohol or pushing physical and mental powers to the limits. Showing general doggedness is a requirement.
"He pulled seventeen girls last night, he's such a terrier"
"I drank twenty pints, didn't have any sleep and now I'm at work, I'm such a terrier"
" won't have a blue WKD thanks, I'm far too terrier-like"