The figure A is, of course, a square. Figure B is an oblong, or a rectangle. Figure C is a rhombus. Figure D is a trapezium (sometimes called a trapeze or trapezoid). And figure E is a parallelogram.
The only figure defined here that Euclid actually uses is the square. The other names of figures may have been common at the time of Euclid's writing, or they may have been left over from earlier authors' versions of the Elements. Euclid makes much use of parallelogram, or parallelogrammic area, which he does not define, but clearly means quadrilateral with parallel opposite sides. Parallelograms include rhombi and rhomboids as special cases. And rather than oblong, he uses rectangle, or rectangular parallelogram, which includes both squares and oblongs.
Squares and oblongs are defined to be "right-angled." Of course, that is intended to mean that all four angles are right angles. Sometimes Euclid's definitions are too brief, but the intended meaning can easily be determined from the way the definitions are used. In particular, proposition I.46 constructs a square, and all four angles are constructed to be right, not just one of them.
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