Phase 1: Planning and securing team leads. This is done in the #wordpress-dev chatroom. The release lead discusses features for the next release of WordPress. WordPress contributors get involved with that discussion. The release lead will identify team leads for each of the features.
Phase 2: Development work begins. Team leads assemble teams and work on their assigned features. Regular chats are scheduled to ensure the development keeps moving forward.
Phase 3:Beta. Betas are released, and beta-testers are asked to start reporting bugs. No more commits for new enhancements or feature requests are carried out from this phase on.
Phase 4: Release Candidate. There is a string freeze from this point on. Work is targeted on regressions and blockers only.
Phase 5: Launch. WordPress version is launched and made available in the WordPress Admin for updates.
The launch is often followed soon after by a point release as bugs are reported and squashed.