Nginx ("engine x") is an HTTP web server that also works as a reverse proxy, content cache, load balancer, TCP/UDP proxy and mail proxy. It supports TLS, HTTP/2, WebSockets and gRPC, among other things. Organisations use it to serve static content, distribute traffic across servers and terminate TLS for back-end applications. Nginx is self-managed software that you run on your own servers or in your own container environment. The paid NGINX Plus, together with commercial support and training, is provided by F5.
The core software is open source under the BSD-2-Clause licence. Nginx was originally written by Igor Sysoev and has been owned since March 2019 by F5, Inc., a US company headquartered in Seattle. Development of the project therefore sits with a company under US jurisdiction, which is relevant to CLOUD Act considerations for commercial products and support. Because you host the software yourself, you decide where traffic and data are processed.