Web Application Server (WAS or WEB AS) is a component of the NetWeaver solution which works as a web application server to SAP solutions. from SAP points of view the (WAS or WEB AS) is the foundation on which most of their product range runs.
Its basic function is to allow web development based on SAP standard solutions (usually developed under the ABAP program language, but in the newer versions also in Java programming language).
With Web AS, it is possible - for example - to publish queries, programs and ABAP applications in a web environment but linked and based in a SAP solution infrastructure. The newer versions of the (WAS or WEB AS) also support open standars like Java programming language.
From the versions 6.20 and > it is posible to create ABAP only, Java Platform, Standard Edition only or mixed enviroments.