A Software Release is usually a deployable software package that delivers planned features and is aimed to launch at specific date.
Agile emphasizes on frequent, valuable, and working delivery of software. A release can be the result of multiple iterations of Sprints. Its progress remains independent of sprints though. Each team defines their own delivery process, depending on their needs. Release board helps you plan and manage release contents. You can customize Release Board layout and columns according to your process.