What the beta symbol means
Beta (β, capital Β) is the second letter of the Greek alphabet, and together with alpha it gave us the word "alphabet". Because it comes second, beta often marks the second version or the second kind of something.
In finance, a stock's beta compares its swings with the whole market. A beta of 1 moves in step with the market, above 1 swings more and below 1 swings less. In software, a beta release is the test version that follows alpha and comes before the final launch.
In physics, beta particles are the electrons or positrons given off in beta decay, written β⁻ and β⁺, and β also stands for speed as a fraction of the speed of light. In statistics, β is the chance of a type II error, so a test's power is 1 − β, and regression coefficients are written β₀, β₁ and so on. Biology has beta-carotene, beta-blockers, the beta cells in the pancreas that make insulin, and the β-sheet shape of proteins.
β is not ß: the eszett mix-up
The German letter ß (eszett, or sharp s) looks a lot like β, and it is what many shortcuts actually type. On a Mac, Option + S gives ß, and on Windows Alt + 225 gives ß, not beta. In some fonts the two are nearly identical, but search engines, spell checkers and screen readers treat them as different letters.
Unicode also has ϐ, a curled form of beta kept for older texts and math, plus small raised and lowered betas (ᵝ, ᵦ) for superscripts and subscripts. For normal Greek or science writing, copy the plain β.
How to type β
Windows has no Alt code for β. In Word, type 03B2 and press Alt + X, or insert an equation and type \beta followed by a space. In Google Docs, use Insert > Special characters and search "beta".
On a Mac, open the Character Viewer with Control + Command + Space and search "beta", or switch to the Greek keyboard, where the B key types β. Phones work the same way: add a Greek keyboard, or simply copy β from this page.
In LaTeX, write \beta (capital beta is just B). In HTML, use β. For more letters see Greek letters, and for statistics symbols such as σ see the standard deviation symbol page.