A more thorough explanation:

Definition: Separability is a legal concept used to determine whether a design in a functional object can be protected by copyright law. It is based on whether the artistic appearance of the design can be separated from its useful function.

For example, if a lamp has a unique and artistic design, but the design is necessary for the lamp to function properly, then the design may not be protected by copyright law because it is not separable from the lamp's function. However, if the design is purely decorative and not necessary for the lamp to work, then it may be protected by copyright law because it is separable from the lamp's function.

Some courts use a strict physical separability test, which means that the design must be physically separable from the object's function. However, most courts use a conceptual separability test, which means that the design must be conceptually separable from the object's function.