In Projects to Products, Mik Kersten divides flow items in software products in four: features, defects, risks, and debt.
If you only count features added and bugs fixed – changes visible externally – then you neglect the other outcome of our work: the next version of the team+software.
I prefer to think of “technical debt” work as groundwork for future changes. I like Kersten’s suggestion to do more of this at the beginning or a release cycle, while preparing to add a lot of features.
Pretending that software is “done” at the end of a project is dangerous. Naming risks and technical debt as part of the output of flow makes caring for our future explicit.