Bug leakage: Bug leakage is something, when the bug is discovered by the end user/customer and missed by the testing team to detect while testing the software. It is a defect that exists in the application and not detected by the tester, which is eventually found by the customer/end user.
Bug release: A bug release is when a particular version of the software is released with a set of known bug(s). These bugs are usually of low severity/priority. It is done when a software company can afford the existence of bugs in the released software but not the time/cost for fixing it in that particular version.