Technical debt is a term developers use to refer to all of the annoying thorns they need to deal with because of past decisions someone made in their codebase and architecture. In software engineering, there are quick ways to do things and there are right ways to do things, and the two don’t always overlap. You also don’t always know which is which.
Technical debt can slow developers down or even prevent new features from being built entirely. It’s also something you can (usually) undo with focused time and effort, which we call “paying down debt.”