I would say: technical debt is anything that makes the system more expensive to maintain (and grow) over time, and becomes more expensive to fix the longer you

I would say: technical debt is anything that makes the system more expensive to maintain (and grow) over time, and becomes more expensive to fix the longer you leave it. If it's just a bad or incomplete aspect of the system, that's not sufficient. It has to become more expensive over time. So e.g. lack of functionality isn't tech debt, but a bad abstraction is usually tech debt.