SOH CAH TOA is a way to remember the definitions of sine, cosine, and tangent.

These functions are defined by the sides of a right triangle,

$\sin \theta = \dfrac{\text{opposite}}{\text{hypotenuse}}\qquad$ Sine is Opposite over Hypotenuse (SOH)

$\cos \theta = \dfrac{\text{adjacent}}{\text{hypotenuse}}\qquad$ Cosine is Adjacent over Hypotenuse (CAH)

$\tan \theta = \dfrac{\text{opposite}}{\text{adjacent}}\quad\qquad$ Tangent is Opposite over Adjacent (TOA)