Part of the The Software Cycle, a release is a software milestone or tested programming benchmark that is set for distribution. A release is usually accompanied by a change log or version history. A release is usually accompianed with a development status such as 1.0, beta, alpha.
A Release Candidate is software that has developed so that it is almost completely ready to be released. A pirated release of intellectual property other than software, like music or games, which is cracked and available on the software's day of release, is called a zero day. A release that has unauthorized distribution of the final product, before the official set day of release, is called a pre-release.