Bug Leakage:
When end user discovered a bug which can be detected by the testing team. Or when a bug is detected which can be identified in the previous build then this is called as Bug Leakage.
Bug release:
when a build is given to the testing team with identifying that defect is present in the release. The priority and severity of the bugs are low. It is done when a client wants the application on the time. A client can tolerate the bug in the released then the delay in getting the application and the cost involved in removing that bug. These bugs are mentioned in the Release Notes handed to the client for the future improvement possibilities.