What exactly is Real Ale?
From the Oxford English Dictionary: "Real ale is a name for draft (or bottled) beer brewed from traditional ingredients, matured by secondary fermentation in the container from which it is dispensed, and served without the use of extraneous carbon dioxide."

What's the definition of Real Ale?
Real ale must be alive when it is drunk. This is the fundamental definition. The alternative is pasteurisation. (i.e. killing off the yeast before the beer leaves the brewery.) Real ale continues to ferment in the cask or bottle after leaving the brewery. This process is known as secondary fermentation. As the fermentation proceeds after putting into casks (cask conditioned) or bottles, (bottle conditioned) the carbon dioxide produced is dissolved into the liquor and gives the beer a natural measure of condition. If the yeast is killed off before casking, then CO₂ has to be added to make the beer fizz.

What's so special about real ale?
The secondary fermentation allows the complex and interesting flavours to develop and produce a beer of far more character and taste than non-real or keg versions. Because real ale doesn't use extraneous gas, real ale will not bloat you like keg beer does.

How do I know if a beer is "real"?
Look for the words "real ale" or "cask conditioned". For most people the handpump is the sign of real ale but things aren't always that simple. Some unscrupulous brewers and pubs use what looks like a handpump but is just a keg dispenser. Sometimes real ale is served with added gas rendering it "non-real". In certain parts of the UK (West Midlands, North West) it is quite common for real ale to be dispensed with an electric pump. If in doubt though just ask. Bottled real ales are invariably marked "Bottle Conditioned" and you may well be able to see sediment. The following are not real and are keg beers: all Nitro Keg such as Caffreys and Guinness, tins and the majority of bottled beers. If it is served through a tiny plastic tap attached to a fancy bar mounted advertising box or array of taps on a brass frame then it is not real.

The above FAQ has been derived from the excellent uk.food+drink.real-ale FAQ.