What is backbone in wine?

What is meant by ‘backbone’ when describing a wine? Or is this just one of those things wine tasters say to impress their friends? 

It’s very hard to describe tastes accurately, so all these wine-tasting terms are an attempt to put into words what the taster experiences. (Can you describe the flavour of a potato?) A good wine should consist of a fine balance between the various components, such as acidity, fruit flavours, tannins and, in some cases, wood. If there is not enough acidity, the wine will be merely flabby and characterless. The tannin in wine acts as a preservative, but also gives it a slightly mouth-puckering astringency. 

A flabby wine leaves a sticky aftertaste in the mouth, while a balanced one will leave you with a fresh, clean palate. When the acidity and astringency are present in just the right amounts to add excitement without masking the fruit flavour, we say the wine has ‘backbone’.