α

Alpha

Often symbolizes an angle.

β

Beta

Often symbolizes an angle.

ϒ

Gamma

Often symbolizes an angle.

Δ

Delta

An infinitesimally small number, especially in calculus.

ε

Epsilon

An infinitesimally small number, especially in functional analysis.

ζ

Zeta

Occasionally symbolizes an angle.

η

Eta

Occasionally symbolizes an angle.

θ

Theta

Usually symbolizes an angle.

ι

Iota

Rarely used.

к

Kappa

Rarely used.

λ

Lambda

The symbol for wavelength, also used to symbolize a ratio or proportion, especially eigenvalues.

μ

Mu

The symbol for “micro,” or a one-millionth-part; also the symbol for various material constants such as the coefficient of friction.

ν

Nu

Rarely used.

ξ

Xi

Sometimes symbolizes an angle.

ο

Omicron

Rarely used.

π

Pi

The constant value 3.14159..., the ratio of the circumference of a circle to its diameter.

ρ

Rho

The symbol for pressure, and used for some material constants.

σ

Sigma

Used for some material constants.

т

Tau

Rarely used.

υ

Upsilon

Rarely used.

φ

Phi

Often symbolizes an angle or frequency; also the constant 1.618..., the golden ratio.

х

Chi

Sometimes symbolizes an angle.

ψ

Psi

Sometimes symbolizes an angle or frequency.

ω

Omega

Often used for the frequency of an oscillation or rotation, and a number of other physical properties.