A rectangle is a 2-D shape that has four straight sides, four right angles and whose opposite sides are the same length. This means that both oblongs and squares are rectangles. Think about it...

A regular polygon is a 2-D shape that is closed (see polygon), has straight sides, whose sides are all the same length and whose angles are also the same size. You can have a regular hexagon, a regular octagon, etc.

The remainder is the bit that can be left over after you have worked out a division sum.