An Application Delivery Controller (ADC) is a device that manages, optimizes, and accelerates the delivery of applications and services to end users.
It sits between the internet and a data center, ensuring that traffic gets delivered with the best quality of service (QoS) based on a set of pre-determined rules. The ADC handles load balancing, traffic shaping, and application acceleration through caching. It also monitors server status and service levels, presenting administrators with real-time reports and alerting them of any problems. In this way, an ADC helps to provide a more stable, secure, and faster service for end users.