Starting to work on an existing application, on a code base that exists since the beginning of the times, can be daunting. Complicated and complex features, new terms, most likely non-existing documentation, or documentation that is out of date. All that can seem too much. One thing that has always helped me is keeping notes of what I discover over time working with a legacy codebase. “Discovery notes” if you will.

Legacy code has many definitions. It is code without tests. It is code written by someone else. It is code written X time ago. It is obsolete code that is difficult to replace with newer code. It is code that has no documentation. It is all of these things.