Surprised it's not in the Foolasaurus. But in a nutshell, it's a measure of how successful an investment has been based on % price growth. It is basically a measure of how much bigger your position is now than it was when you bought it.

For example, if I purchase a company, such as TMF (not a public company), at $50/share, and that stock price grows to $100/share, that is called a single bagger. My position has doubled in price. If the stock price grows to $150/share, it becomes a double bagger.

It's not an official term, but then again, neither is SpiffyPop, which you will see commonly used to describe an explosion in the stock price, such as what happened this week with Netflix, or a SpiffyPlop, which describes an implosion as you have seen with Apple.

Fuskie
Who hopes this helps...