A few days ago, Oracle released their quarterly patches for currently supported Oracle versions. Now in the past, the DBA had the option of installing the Cumulative Patch Update (CPU) or the Patch Set Update (PSU). Basically, the CPU contains just security patches and the PSU contains security patches and other bug fixes.
Beginning in October 2012, it looks like Oracle made a terminology change. The CPU is now known as the Security Patch Update or SPU. Now “Security Patch Update” is named more correctly in my opinion. But the part I really do not like is that SPU is too close in name to PSU and I know this will trip people up at one point.