Scalability is the capability of a system, network, or process to handle a growing amount of work, or its potential to be enlarged in order to accommodate that growth. This is the fundamental underpinning of cloud computing. Resources can be scaled almost infinitely and billed to the customer for how many resources they are using. Scalability is achieved through different technologies such as elastic networking, storage, and computing. When a system grows by adding servers during peak hours, a form of scalability has been achieved.
in other words
The number of extra belt loops available before Thanksgiving dinner.