nginx - what is forward proxy, reverse proxy

Question

"Ngnix can implement the reverse proxy function of HTTP requests"
So what is a reverse proxy, and how is the corresponding forward proxy defined?
I never quite understand~~~

Answer 1

/search?q=%E5%8F%8D%E5%90%91%E4%BB%A3%E7%90%86

Answer 2

http://jingyan.baidu.com/article/f54ae2fcd895b81e93b84973.html