Definitions:

1. A grade rating a student's work as good but short of excellent. noun
   • My grade on that first paper was a B.
2. A human blood type of the ABO group, containing the B antigen. NOUN
   • She told the doctor in the emergency room that her blood type was B.
3. the 2nd letter of the Roman alphabet noun
   • All of their children's names begin with B.
4. The second constant to appear in an algebraic equation. NOUN
   • If A equals B and B equals C, then A equals C.
5. The seventh tone of a C-major scale. NOUN
   • A song in the key of B.