What type of server Django runserver uses?
It's exactly what it says on the tin - a simple, lightweight web server implemented in Python that ships with Django and is intended for development purposes only. It's not a free-standing web server in its own right and is intended purely for developing applications with Django - you should never use it in production because it simply doesn't offer all the functionality you need in a production web server.
A web server can be implemented in virtually any programming language, and so it makes sense to ship one implemented in Python with Django in order that you can get working with it immediately without having to install something like Apache as well. Most web servers that might be used in production, such as Apache and Nginx, are written in C so it wouldn't really be practical to ship them with Django.
Also, shipping your own development server cuts down on complexity. Apache and Nginx are both complex pieces of software that require a fair amount of configuration, and while there are ways to automate that during development, it's not something you really want to have to deal with when you'd rather be writing code. All you need to get you started is something that will serve static and dynamic content - you don't need a lot of the other functionality required. It's notable that even PHP now ships with a development server.
When you go live with a Django project, you should use of course use a proper web server. It's generally recommended that with Django, in production you should use two web servers, one to serve static content, the other to serve dynamic content, because involving Django in serving static content will slow it down. This sounds odd at first, but it actually makes a lot of sense, because what you do is set one web server to serve all the static content, then have it reverse proxy to the other server, which is running on a non-standard port, and serves all the  dynamic content. The setup I have for my current project is Nginx for the static content, with Gunicorn for the dynamic content.
What type of server Django uses when "runserver" command is ran? Documentation says more or less that it's "lightweight development Web server". Is it for example Apache? Thanks in advance.