Is a server essentially a background process running an infinite loop listening on a port? For example:

while(1){
   command = read(127.0.0.1:xxxx);
   if(command){
      execute(command);
   }
}

When I say server, I obviously am not referring to a physical server (computer). I am referring to a MySQL server, or Apache, etc.

Full disclosure - I haven't had time to poke through any source code. Actual code examples would be great!