Congruent
If one shape can become another using Turns, Flips and/or Slides, then the shapes are Congruent:
Rotation  Turn!  

Reflection  Flip!  
Translation  Slide! 
After any of those transformations (turn, flip or slide), the shape still has the same size, area, angles and line lengths. 
Examples
These shapes are all Congruent:
Rotated  Reflected and Moved  Reflected and Rotated 
Congruent or Similar?
The two shapes need to be the same size to be congruent.
When we need to resize one shape to make it the same as the other, the shapes are Similar.
When we ...  Then the shapes are ...  

... only Rotate, Reflect and/or Translate 
Congruent 

... also need to Resize 
Similar 
Congruent? Why such a funny word that basically means "equal"? Probably because they would only be "equal" if laid on top of each other. Anyway it comes from Latin congruere, "to agree". So the shapes "agree"