Varnish Cache is an open-source HTTP accelerator designed to boost the performance of websites by caching content in memory for reduced load times and efficient resource management. Commonly positioned in front of web servers, Varnish Cache handles client requests by serving cached content when available, thereby reducing server load and improving speed and scalability. It is highly customizable through its Varnish Configuration Language (VCL), allowing users to tailor caching policies to meet specific needs. Suitable for both small websites and large-scale enterprise environments, Varnish Cache is known for its high performance and flexibility.