Definition of pb:
(v) :
(usually intransitive, informal) To set a new personal best.
(n) :
Initialism of peanut butter. [A spread made from ground peanuts.]
(n) :
(sports, speedrunning) Initialism of personal best. [A person's best ever performance at some task to date.]
(n) :
(finance) Initialism of prime broker or prime brokerage.
(n) :
Initialism of parallel bars. [A set of apparatus consisting of two horizontal bars at a small distance apart, upon which acts of swinging and holding and jumping and dips are performed.]
(n) :
Initialism of PowerBook (“family of Macintosh laptop computers”).