Mathematics. the act or process of finding a square equal in area to a given surface, especially a surface bounded by a curve. the act or process of finding an area or calculating an integral, especially by numerical methods. a definite integral.

Definition: 3

Astronomy. the situation of two heavenly bodies when their longitudes differ by 90°. either of the two points in the orbit of a body, as the moon, midway between the syzygies. (of the moon) those points or moments at which a half moon is visible.

Definition: 4

Electronics. the relation between two signals having the same frequency that differ in phase by 90°.

Definition: 5

(maths) the process of determining a square having an area equal to that of a given figure or surface