Oracle "clarifies" Java's release numbering
"clarify" in the loosest sense of the word, this.
Java: keeping it secure was too hard, so we went off and invented a ridiculous new naming scheme to keep us busy and make us feel smart again.
Limited Update releases will be numbered in multiples of 20.
We intend for Critical Patch Updates to continue to use odd numbers. The numbers will be calculated by adding multiples of five to the prior Limited Update and when needed adding one to keep the resulting number odd.
This is best illustrated with an example:
The next Limited Update for JDK 7 will be numbered 7u40, and the next 3 CPUs after that will be numbered 7u45, 7u51, and 7u55. The next release will be a Limited Update 7u60, followed by CPUs 7u65, 7u71, and 7u75.
This numbering scheme will leave several numbers between releases which will allow us to insert releases – for example security alerts or support releases, should that become necessary - without having to renumber later releases.
Java SE - Change in Version Numbering Scheme March 2013 (via SlashDot)