Software as a service (SaaS) is a software application delivery model where a software vendor develops a web-native software application and hosts and operates (either independently or through a third-party) the application for use by its customers over the Internet. Customers do not pay for owning the software itself but rather for using it. They use it through an API accessible over the Web and often written using Web Services or REST. The term SaaS has become the industry preferred term, generally replacing the earlier terms Application Service Provider (ASP) and On-Demand.