Django server details

I have been working with django since 2 years, still confuse with some of the server related concepts of django as follows:-

1. What web server does django use when I run python manage.py runserver?

2. What is wsgi(I know it is web server gateway interface(sets of rules can say protocols) act as an middle-ware for the communication of web server and web application) then wsgi is the server django runs on?