SharePoint has been in the market since 2001 and it is now the best selling server product in Microsoft.
With each release of SharePoint there was new name or abbreviation for the server and there was always the SharePoint service (core/framework of SharePoint) and the SharePoint server.
Here simple diagrams the evolution of the services and its corresponding server.
SharePoint Services (Foundation)
Worth telling that the latest version of SharePoint services is SharePoint foundation 2010 and the server is SharePoint server 2010 and no abbreviation for them ;)