Decoupling is the reduction of dependencies between computational parts.
Coupling is a measure of dependencies between different parts of a computer program.
Decoupling is the reduction of said dependencies, in order to improve code maintainability.
The goal of decoupling is to create a loosely coupled program (also known as "low/weak coupling".
That is because a high/tight/strong coupling program is harder to change since often a change in one part of the code forces changes to other parts of the code as well, causing a ripple effect that can spread throughout the entire code base in worst case scenarios.
The benefit of a a low/loose/weak coupling program is that when a change is needed in one part of the code, it should require no change (or at the very least, as little change as possible) to the other parts of the program - thus making the maintenance of a loosely coupled program easier.
