Elliptical is from the Greek elleiptikos which means "defective." in the sense that it is a less than perfect circle.
The most common usage of "elliptical" is the geometric shape described informally as an oval or an egg shape.
In astronomy "elliptical" is used to describe a type of galaxy that has a vaguely oval shape such as galaxy M87.
Elliptical writing and speaking is characterized by economy and ambiguity. The person's meaning is often in doubt and sometimes described as cryptic.
Elliptical exercise machines are a type of aerobic stepper that use an oval shaped foot pedal path for a smoother, more natural motion.