In geometry, an equilateral polygon has all sides of the same length. By definition a square is always equilateral (see also rectangle):

x x x x 
x x x x 
x x x x 
x x x x

This triangle is also equilateral:

    x 
   x x 
  x x x 
 x x x x 
x x x x x

Any n-sided polygon which has n sides of equal length can be considered an equilateral. Not all equilaterals are convex geometric shapes: consider that for a pentagon two adjacent sides can be reflected in the line segment joining the two extreme vertices.