Two figures are considered to be "similar figures" if they have the same shape, congruent corresponding angles (meaning the angles in the same places of each shape are the same) and equal scale factors. Equal scale factors mean that the lengths of their corresponding sides have a matching ratio. Knowing how to identify similar figures makes it easier to prove geometric theorems and postulates.
There's a difference between similar and congruent figures. Two shapes are congruent when they are the same exact size and have the same angle measurements. Similar figures, on the other hand, do not have to be the same size.
Below is an example of similar shapes:
Although they are different sizes, triangle ABC and triangle DEF are considered similar triangles because they have proportional shapes and angles. Triangle ABC is simply an enlargement of DEF.