Beta \Be"ta\, n. [Gr. bh^ta.]

The second letter of the Greek alphabet, B, [beta]. See B, and cf. etymology of Alphabet.

Note: Beta (B, [beta]) is used variously for classifying, as:
   (a) (Astron.) To designate some bright star, usually the second brightest, of a constellation, as, [beta] Aurig[ae].
   (b) (Chem.) To distinguish one of two or more isomers; also, to indicate the position of substituting atoms or groups in certain compounds; as, [beta]-naphthol. With acids, it commonly indicates that the substituent is in union with the carbon atom next to that to which the carboxyl group is attached.

Source: Webster's Revised Unabridged Dictionary (1913)