Transformations
The three main Transformations are:

After any of those transformations (turn, flip or slide), the shape still has the same size, area, angles and line lengths. 



If one shape can become another using Turns, Flips and/or Slides, then the two shapes are called Congruent. 
Resizing
The other important Transformation is Resizing (also called dilation, contraction, compression, enlargement or even expansion). The shape becomes bigger or smaller:
If you have to use Resizing to make one shape become another then the shapes are not Congruent, they are Similar.
Congruent or Similar
So, if one shape can become another using transformation, the two shapes might be Congruent or just Similar
If you ... 

Then the shapes are ... 
... only Rotate, Reflect and/or Translate 

Congruent

... need to Resize 

Similar

