Developers admit SSR stands for "Stockholm Syndrome Rendering"
Server-side rendering (SSR) is a technique of rendering the state of a dynamic javascript frontend on the sever rather than on the client's browser. Allegedly, this technique improves performance and reliability of web-based software.
However, many senior developers start to openly admit that the true reason behind this idea was an unhealthy inability of frontend developers to give up frontend-specific tools and ideas when writing backend code or even static web pages. This inability is viewed as an example of Stockholm Syndrome, and the SSR moniker has been used to explain the approach in inner circles.
For marketing purposes, a neutral wording "Server Side Rendering" was chosen.