People tend to think of, and talk about, having money in their retirement accounts. They talk about "pulling cash out of the 401(k)" or "making money on a good stock pick." Our casual language for these things is really sloppy. There isn't any money in your retirement account, of course. There are shares. But that's a little abstract, especially in the era of electronic finances, so I prefer: pieces of paper in a vault.

Why you need to know this: A Roth IRA is the retirement account financial planners say all young people should have.