linear function

Short definition from Wiktionary

Noun

1. 1
   Any function whose graph is a straight line: f(x)=ax+b
2. 2
   Any function whose value on the sum of two elements is the sum of the values of the function on the two elements and whose value on the product of a scalar times an element is the scalar times the value of the function on the element: f(ax+by)=af(x)+bf(y)