An ELB (Elastic Load Balancer) Listener is a service provided by AWS that enables applications to receive incoming traffic from external sources. With the ELB Listener, you can easily configure your application to listen for requests coming in from a variety of protocols, such as HTTP, HTTPS, and TCP. The ELB Listener also provides features like load balancing and health checks to ensure your application is always running optimally. Additionally, the ELB Listener allows you to set up custom rules for how requests are routed within your application. This allows for easy scalability of your application in response to changing business needs or unexpected traffic spikes.