A transformation is a function that changes a figure in a particular way — it can change the position, size, or orientation of a figure. The original figure is called the preimage and the figure produced is called the image of the transformation. A prime symbol is often added to the label of a transformed point to denote that it is an image.

Transformations are sometimes expressed as a mapping because they map the inputs to the outputs. Note that an input can be a single point. T(x,y) → (x',y') Here, T is the transformation, x and y are the coordinates of the point of the preimage, and x' and y' are the coordinates of the point of the image.