trigonometric function: function of an angle expressed as a ratio of the length of the sides of right-angled triangle containing the angle
function: (mathematics) a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)
volt-ampere: a unit of electrical power in an AC circuit equal to the power dissipated when 1 volt produces a current of 1 ampere