Release planning refers to planning activities used to estimate when software will be released into product use. Activities include projecting the level of effort in terms of the number of iterations that will be necessary to deliver the desired features. This is typically done by extrapolating the development team's performance on the basis of its velocity.
A release planning meeting that brings together all parties that have a stake in the outcome and have some kind of delivery responsibility to achieve the release is often necessary to produce a viable release plan. This is especially the case when several development and non-development production efforts are running in parallel with possible dependencies.
Release planning is one of the five levels of planning.
Related links: Release Planning