3b Definition

abbreviation
Third base.
Webster's New World
Third baseman.
Webster's New World
(baseball) Third base, third baseman.
Wiktionary

(baseball) Triple, a baseball statistic indicating a runner has safely advanced to third base.

Wiktionary

(UK) A grade of pencil with lead that makes darker marks than a pencil grade 2B but lighter marks than a pencil of grade 4B.

Wiktionary