A web accelerator provides optimisation and security to web traffic, both HTTP and HTTPS (secure) by focussing in two key areas:
Client facing optimisations include page compression, content and image rewriting and optimisation, CSS and JS minification and much more. This is intended to ensure your clients page loads faster.
Server facing optimisations are designed to offload your web servers with technologies like caching, compression offloading, SSL offloading as well as reducing the time it takes for pages to be generated, thus decreasing your clients load times.
Aside from optimisation the web accelerator also has the task of protecting your web servers from attacks and DoS attempts, as well as delivering content no matter what. Web accelerators (such as Snapt’s) will often be able to serve content even if all your web servers have failed.