Web Application— sometimes called a Web app is an application that's accessed with a Web browser over a network such as the Internet or an intranet. Another term associated with Web App,  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. From Wikipedia

Web applications provide students, teachers and parents wonderful tools and resources in education that are by and large free!  As schools increasingly use Internet and Intranet services, the ongoing blurring of open source software and web applications will serve to support teaching and learning across the curriculum.