Shapes are congruent when they have all the same side lengths and angles. This means they are exactly the same in size and shape, even if their orientation or position is different.
On the other hand, shapes are similar when they have the same angles, but different side lengths. The side lengths must change by a consistent ratio (also known as a scale factor) for shapes to be considered similar.
Examples
The triangles on the left are congruent. They have identical side lengths and angles.
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