Meaning of B in English

B BrE AmE , b /biː/ noun ( plural B’s , b’s )

1 . [uncountable and countable] the second letter of the English alphabet

2 . [uncountable and countable] the seventh note in the musical ↑ scale of C ↑ major or the musical ↑ key based on this note

3 . [countable] a mark given to a student’s work to show that it is good but not excellent:

I got a B in history.

4 . [uncountable] used to refer in a short way to one of two different things or people. You can call the first one A.:

the advantages and disadvantages of choosing product A or B

⇨ plan B at ↑ plan 1 (6)

5 . B4509/B1049 etc the name of a road in Britain that is smaller than an ↑ A-road

6 . [uncountable] a common type of blood

⇨ from A to B at ↑ A 1 (6), ⇨ ↑ B-movie , ↑ B-side , ↑ B-road

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.