Sine (sin)
In a right triangle, the sine of an angle is defined as the ratio of the length of the side opposite the angle to the length of the hypotenuse.
Cosine (cos)
In a right triangle, the cosine of an angle is defined as the ratio of the length of the adjacent side to the length of the hypotenuse.
Tangent (tan)
The tangent of an angle is defined as the ratio of the sine of the angle to the cosine of the angle.
Cosecant (csc)
The cosecant of an angle is defined as the reciprocal of the sine of the angle (1/sin).
Secant (sec)
The secant of an angle is defined as the reciprocal of the cosine of the angle (1/cos).
Cotangent (cot)
The cotangent of an angle is defined as the reciprocal of the tangent of the angle (1/tan).