The degree to which something can work under heavy load.

Scalability is the ability of a computer application or product (hardware or software) to continue to function well when it (or its context) is changed in size or volume in order to meet a user need.

Typically, the rescaling is to a larger size or volume.

The rescaling can be of the product itself (for example, a line of computer systems of different sizes in terms of storage, RAM, and so forth) or in the scalable object's movement to a new context (for example, a new operating system).

For example, does a piece of software work as well with one million users as it does with 100? If so, the software is said to "scale."