1. Similar
Similar means that the corresponding sides are in proportion and the corresponding angles are congruent.
(same shape, different size)

2. There are 3 ways to prove triangles similar:
1) AA Similarity
2) SSS Similarity
3) SAS Similarity

3. AA Similarity
Two triangles are similar if 2 pairs of corresponding angles are congruent.

4. SSS Similarity
Two triangles are similar if 3 pairs of corresponding sides are in proportion to one another.

5. SAS Similarity
Two triangles are similar if 2 pairs of corresponding sides are in proportion and the corresponding angles are congruent, in between the 2 sides.