NEW YORK (AP) — When Detroit became the biggest city in U.S. history to file for bankruptcy last month, it turned public attention to the municipal-bond market, where cities and states go to borrow money. Was this sleepy, often-overlooked area of the financial world actually dangerous?

Like other cities, Detroit borrowed from investors to pay for roads, sewer lines and an array of other projects. Now Detroit says it can't afford to pay bond investors all of their money back.

Even if you don't own any muni bonds, it's important to understand what they are and how they work. They're what your city uses to keep itself running, but it can be tough to cut through the jargon and heated claims surrounding Detroit's bankruptcy. To help, here's a look at the nuts and bolts of what finance types call munis: who owns them, how they work and just what they are, anyway.