A mnemonic for the relationships between the sine, cosine and tangent functions to the lengths of the "opposite", "adjacent", and "hypoteneuse" sides of a right triangle. (The way it was told to me, "Sohcahtoa" was the name of a mathematician Indian chief.)

SOH: Sine = Opposite / Hypoteneuse
CAH: Cosine = Adjacent / Hypoteneuse
TOA: Tangent = Opposite / Adjacent