There are excellent articles explaing what a “back end” is in software development written 9/4/2021: https://www.codecademy.com/resources/blog/what-is-back-end/
“A back end is a combination of servers and databases. Servers control how users access files. Databases are organized and structured collections of data.”
This is a good definition from the article. Can you update it to reflect the changes from serverless architecture and other industry technology change?
It can include other components that make up a back end, such as api services, and 3rd party components.