I use the term Technical Debt and relate it directly to something they understand - Corporate Debt. Technical Debt is like taking out a loan. You pay interest on it. E.g., you can build a new factory and pay for it outright or you can get a loan for it. If you get a loan you will actually pay more for it in the long term, but it makes sense financially *if the terms are right*. 

However, if you are paying 25% interest on such a loan you put yourself into a non-sustainable position. This is the same with technical debt. Sometimes it makes sense to take on some technical debt. However, there comes a point where the interest is too high and it needs to be paid off. Some techincal debt is like a home loan and some it is like credit card debt. In emergencies credit card debt is an important and valuable asset. However, it can also break the bank (or household if you choose) if used unwisely. 

Another example: you can pay $10,000 for a marketing mail drop to garner more leads for sales in the future. You are paying off "sales debt". This is an expense with long term payoff. Equate this to why you would want to "spend" money now refactoring a piece of code. In both cases there is no immediate payoff, but you are setting yourself up for better performance in the future.

I tend to use the term "xxxx debt" as an analogy when talking to whomever the target audience is. E.g., Operational Debt - The printing press we have now works well, but by stopping production for one day (or one week) and upgrading to a new machine we can increase output by 25%.