Two figures are said to be similar when all corresponding angles are equal and all distances are increased or decreased in the same ratio, called the ratio of magnification. A transformation that takes figures to similar figures is called a similarity. In other words, figures are similar if they are identical in shape, although not necessarily the same size. Two figures are directly similar when all corresponding angles are equal and described in the same rotational sense. This relationship is written as A ~ B. (The symbol ~ is also used to mean it is the same order of magnitude as and is asymptotic to.) Conversely, two figures are inversely similar when all corresponding angles are equal and described in the opposite rotational sense. The diagram below illustrates what several similar shapes look like.
“Similar.” From Wolfram MathWorld, mathworld.wolfram.com/Similar.html.