JBoss is an open-source application server that implements the Java EE (Enterprise Edition) specifications. It allows developers to build, deploy, and host Java applications and services, providing a robust platform for enterprise-level solutions. Originally developed by JBoss, Inc., it was later acquired by Red Hat in 2006. JBoss is known for its flexibility, scalability, and support for various programming models, making it a popular choice for businesses looking to create dynamic web applications and services.