Apache ActiveMQ is an open-source message broker that enables applications to communicate with each other by sending messages through queues and topics. It supports multiple messaging protocols, including JMS, AMQP, MQTT, and STOMP, making it versatile for various integration scenarios. ActiveMQ is widely used in enterprise environments to decouple application components, improve scalability, and ensure reliable data transmission. In cybersecurity, securing ActiveMQ is crucial, as vulnerabilities or misconfigurations can expose sensitive data or allow unauthorized access. Common security measures include enabling authentication, using encrypted connections (SSL/TLS), and applying access controls to protect message integrity and confidentiality.