A release demo showcases the latest pre-launch developments to a product or software project. Agile development teams tend to hold a release demo at the end of every iteration, designed to keep everyone involved up to speed with how each iteration is going, and how the project as a whole is progressing.
Release demos can be very small, just including a select bunch of stakeholders, or can include the entire organization, depending on the status of the project, the current iteration or the size of the team.