SSS (Side-Side-Side) Similarity

SSS similarity theorem is a theorem used to prove similarity of triangles. It states that

If two triangles have corresponding sides in equal ratio, then the two triangles are similar.

That is, if two triangles $ABC$ and $DEF$ have

$$\frac{AB}{DE} =\frac{BC}{EF}= \frac{CA}{FD}$$

then the two triangles are similar.