General:
* Quadrilateral: A four-sided polygon. This is the most general term, as all rectangles are quadrilaterals.
* Four-sided figure: Similar to quadrilateral, but less formal.
* Oblong: This specifically refers to a rectangle with unequal sides.
Specific:
* Square: If the rectangle has all sides equal, it's a square.
* Parallelogram: A quadrilateral with two pairs of parallel sides. Rectangles are a special type of parallelogram.
* Rectangular: This adjective describes something shaped like a rectangle.
Figurative:
* Box: This is more of a metaphorical use, referring to a rectangular shape.
* Panel: Often used for a rectangular section of a larger surface.
The best word to use depends on the context and the specific characteristics you want to emphasize.