Ask HN: Is my terminology correct?

I'm building out a website with the following setup:

Client <--> mysite.com <--> Nginx <--> Flask (Python) Website <--> DB

Where Nginx (Machine #1) either serves a static resource (js, css, etc...), or reverse proxies the request to my Flask application (Machine #2) which does any necessary communications with the database (Machine #3), and returns whatever html content was requested. Reason for this is because Nginx is great for serving static resources so I wanted to put that in front of my Python code.

Question: How do I classify them?

Is it: Nginx - Web Server, Flask - App Server, MySQL - DB Server

or: Nginx - Web Server, Flask - Web Server, MySQL - DB Server

or: Nginx - Proxy Server, Flask - Web Server, MySQL - DB Server