Is it possible for a quadrilateral to have exactly 3 sides of equal length. I was just wondering. It would most likely be an Isosceles trapezoid.

An isosceles trapezoid would be one option. There could also be just a regular old quadrilateral. Take three toothpicks and touch their points together. If the angles are the same, you have a isos. Trap. Different you will have a quad. Play with it and you'll see what I mean.