The Web has grown a mindboggling amount in the number of sites, users and implementation capabilities since the first website went live in 1989. Web development is the concept that encompasses all the activities involved with websites and web applications.
Python can be used to build server-side web applications. While a web framework is not required to build web apps, it's rare that developers would not use existing open source libraries to speed up their progress in getting their application working.
While not Python-specific, Mozilla put together a Learning the Web tutorial for beginners and intermediate web users who want to build websites. It's worth a look for general web development learning.
The Evolution of the Web visualizes how web browsers and related technologies have changed over time as well as the overall growth of the Internet in the amount of data transferred. Note that the visualization unfortunately stops around the beginning of 2013 but it's a good way to explore what happened in the first 24 years.
Web development involves HTTP communication between the server, hosting a website or web application, and the client, a web browser. Knowing how web browsers works is important as a developer, so take a look at this article on what's in a web browser.
Three takeaways for web developers after two weeks of painfully slow Internet is a must-read for every web developer. Not everyone has fast Internet service, whether because they are in a remote part of the world or they're just in a subway tunnel. Optimizing sites so they work in those situations is important for keeping your users happy.