Difference between report builder and report designer

Report Builder is a web-based tool to create reports. Report Builder is assessable through the Report Manager so the reports developed are bydefault stored in the Server but reports developed using Report designer of BIDS available in MS Visual Studio can be stored as RDL Files in the local or can be stored in the server. There is no compulsion as such.
Report Builder is basically used by the end-users for developing some basic reports with little features as compared to the large functionality of Report Designer in BIDS which is mainly used by developers.
A report builder looks more or less like some Microsoft Office tools.