JBoss Application Server is an open-source Java-based application server that provides a platform for building, deploying, and hosting enterprise applications. It supports the Java EE (Enterprise Edition) specifications, allowing developers to create scalable and robust applications using familiar Java technologies. Originally developed by JBoss, Inc., it is now part of the Red Hat portfolio. JBoss Application Server is known for its flexibility, modular architecture, and support for various programming models, making it a popular choice for businesses looking to implement Java applications in a reliable environment.