In this applet, you can find the names for special four sided shapes by changing the shape on the grid. (This is edited for British English from No's applet http://tube.geogebra.org/material/simple/id/2681129)
How many different words are there in the applet for four sided shapes? Make notes: what makes a square a square? Do the angles have to be the same? Can the lengths be different? Are the diagonal lengths the same or different? Your task is to create definitions for EACH of the names (square, rectangle, etc.). Be sure to share what you notice about the lengths, angles and diagonals. Be ready to explain to the class why you think your definition is right.