IBM WebSphere Application Server is a platform that provides an environment for applications to run in a secure, scalable and highly available manner. It offers advanced features such as Java Enterprise Edition support, load balancing, clustering, and high availability. Developers use this platform to deploy, manage, and integrate various applications across different operating systems and platforms. It is widely used in enterprise-level applications and offers multiple deployment models, including on-premise, cloud, and hybrid. IBM WebSphere is a specialized skill that requires expertise in configuring and managing application servers, applications, and related infrastructure.