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The eighth Greek letter, the default name for an angle.
Also known as: Greek letter theta, Theta symbol, Angle symbol, θ
Theta is the letter mathematics reaches for when it needs an angle. In trigonometry and polar coordinates it is so consistently the angle that a reader meeting an unlabelled θ can generally assume one.
Is a letter of the Greek alphabet before it is a symbol: what it denotes is fixed by the field it appears in, not by the character itself. The uses below are the documented conventions, not competing definitions.
Contexts: Mathematics
In trigonometry, denotes an angle — the near-universal convention.
Contexts: Mathematics
In polar and spherical coordinates, denotes the angular coordinate.
Contexts: Mathematics
In statistics, denotes an unknown parameter being estimated.
Contexts: Mathematics
Is unusually stable for a Greek letter: unlike alpha or lambda, a reader meeting theta in a mathematical context can usually assume an angle without further information.
Contexts: Mathematics
An oval standing upright with a single horizontal bar across its middle.
Both are a rounded outline crossed by a short stroke. The resemblance is real but the contexts are wholly separate — one appears in formulae, the other on hardware.