Alfresco Share (share.war) is a web application that runs on the Java Platform. In a development environment it is usually deployed and run on top of Apache Tomcat. Share is an option for the front end of the Alfresco Content Service offering.
Share is built up of a main menu that leads to pages, which is similar to most other web applications that you might come across. However, there is one special page type called Dashboard that contains Dashlets. A Dashboard page can be configured by the end-user, who can add, remove, and organize the Dashlets on the page.
More about Share: http://docs.alfresco.com/community/concepts/dev-extensions-share-architecture-extension-points.html