In a general sense the term 'applying' is used for any planet moving towards the conjunction or aspect of another. In strict terminology, a planet is said to be 'in application' or 'applying' to another when the planets are within orb of aspect and moving towards perfection (exactness). Planetary motion must be considered, for if a planet is retrograde an aspect that appears to be applying towards exactness may in fact be separating, and if a planet is about to turn retrograde an aspect that is currently in a state of application may fail to perfect.

In an aspect, the planet moving more quickly is said to be making the application or casting the aspect. The slower planet receives the influence.