What is CPU (Critical Patch Updates/Cumulative Patch Updates) Patch?

Oracle release Critical Patch Updates (CPU) every quarter to fix bug (issue) in existing release (ie: 10.2.0.4). We use opatch utility to apply CPU patches. We can rollback CPU patches. It can be call one-off patch.

What is PSU (Patch Set Update) Patch?

PSU patch are consist of CPU patch. This content of all previous CPU Patches and each PSU is limited from 25 to 100 new bug fixes. PSU are referenced by their 5th place in the Oracle version numbers which makes it easier to track  (e.g. 10.2.0.3.1) and will not change the version of oracle binaries (like sqlplus, exp/imp etc.)

What is Patch Set?

Patch sets are a mechanism for delivering fully tested and integrated product fixes. Patch sets provide bug fixes only; they do not include new functionality and they do not require certification on the target system.

We use runinstaller to apply patch set and nust me need execute catpatch.sql script.