A journal is a form of diary. If you keep a journal, you probably record in it all the things that happen to you. The i5 server is also capable of keeping a journal and recording events in it. For this reason, journaling can be thought of as making a permanent record of some of the things that happen in the computer.
Although journaling can be used to record any event, it is usually reserved for the recording of changes in key database files. Unlike journals that people keep, the i5 can keep many journals simultaneously.
Once the system records an event in a journal, it is safe from tampering. Even QSECOFR cannot alter it by any means.