IBM WebSphere MQ is a messaging middleware software that enables applications to communicate with each other across different platforms and systems. It provides reliable, secure, and scalable messaging services for enterprise applications, allowing messages to be sent and received between applications without direct coupling. A specialized skill in IBM WebSphere MQ involves expertise in setting up, configuring, and managing MQ infrastructure, as well as troubleshooting and resolving issues related to message flow, security, and performance.