There are two types of overriding operations: 'override and commit' and 'override and update'. The overriding means replacing one resource with another (local with remote for updating and vice versa for committing). To start these actions click on 'Override and Commit' or 'Override and Update' of resource pop-up menu items in the 'Synchronize View'.
The user should be very accurate while using this operations to avoid ignoring some valuable changes.
SVN Workspace Synchronization