What is the meaning of β?

a voiced bilabial fricative or, occasionally, approximant.

[β]-fricated release of a plosive (e.g. [bᵝ], sometimes implying an affricate [b͜β]); [β]-coloring; or a weak, fleeting or epenthetic [β].

Used in chemical nomenclature to refer to the second of several isomers, positions or variations.

Stone–Čech compactification

beta ray, beta particle, beta radiation

speed parameter,

The 2nd letter of the Arvanitic Albanian Greek-script alphabet.

Lower-case beta (βῆτα), the second letter of the ancient Greek alphabet. It represented the voiced bilabial plosive: /b/ and later the voiced labiodental fricative /v/. It is preceded by α and followed by γ.

Lower-case beta (βήτα), the second letter of the modern Greek alphabet. It represents the voiced labiodental fricative: /v/. It is preceded by α and followed by γ.

Source: wiktionary.org