Terminology
New or Recently Introduced Terms 
 Diagonal (e.g., the line drawn between opposite corners of a quadrilateral)

 Perimeter (the boundary or length of the boundary of a two-dimensional shape)

 Regular polygon (a polygon whose side lengths and interior angles are all equal)

 Tessellate (to tile a plane without gaps or overlaps)

 Tetromino (a shape composed of four squares that are connected so that every square shares at least one side with another square)