Trigonometry is a branch of mathematics that deals with the relationships between angles and sides of triangles. The term TRIG. FUNCTION refers to the various functions used in trigonometry, such as SINE (4 letters), SEC (3 letters), ARCTAN (6 letters), SINH (4 letters), ARCSIN (6 letters), SIN (3 letters), ARCSINE (7 letters), COSEC (5 letters), COS (3 letters), COTAN (5 letters), COT (3 letters), SECANT (6 letters), TANGENT (7 letters), COSINE (6 letters), TAN (3 letters), CSC (3 letters), CTN (3 letters), and TANH (4 letters). These functions are used to calculate the angles and sides of triangles, as well as other shapes.