What is the difference between websphere and weblogic?

Both are brand names of Software products made by their respective manufacturers i.e. IBM and BEA, however people generally refer to their Application Servers written in compliance with the J2EE specifications maintained by SUN. In that sense both are similar products and work on Java. However there may be differences between both in the way they are implemented and the J2EE features that they offer as well as additional value adds. Those would be too much to list here and suggest that you visit the respective sites of the Vendors.

(These are not just application servers actually but entire suite of products, but generally people mean 'Application Servers')