We say that two shapes are congruent if they are both the same shape and exactly the same size.
We say that two shapes are similar if they are both the same shape not necessarily the same size.
Being congruent is a special case of being similar. If two similar shapes are exactly the same size, they are congruent, but they are still considered to be similar as well.
All congruent shapes are also similar. Not all similar shapes are congruent.
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