This is an article I wrote for the CAMRA column in our local papers. It probably simplifies the issue, but it is written with the general reader in mind, not beer enthusiasts who read beer blogs - such as me!
I know that some of the terms used by beer lovers can be confusing, particularly 'real ales', 'keg beers' and 'craft beers'. To begin with real ales: these are brewed in such a way that they finish their fermentation in the barrel, are not filtered or pasteurised, and are served without gas pressure.
Old-fashioned keg beers were brewed to a certain point, pasteurised to stop the fermentation process, filtered, and served using carbon dioxide (CO2) pressure from a gas cylinder. Modern smoothflow beers are similar, except that the gas is a mixture of CO2 and nitrogen.
Why did brewers go for keg beers? They could be produced in huge quantities, were never cloudy, and there was little waste. They were easy to serve and their taste was consistent: at best bland, or at worst downright unpleasant, depending who'd brewed it. At one time it looked as though keg might take over the whole beer market, which led to the founding of CAMRA in the 1970s.
So far so good: real ales are naturally-produced products, while keg beers and smoothflow are not, which was quite straightforward to understand until the arrival of craft beers in recent years. These beers are skilfully brewed using good ingredients without filtering or pasteurisation, and most would qualify as real ales until the point when they are served, which is done using gas pressure. Because of this, they do not fit the description of 'real ale' as defined, not only by CAMRA but also by most modern dictionaries. This means that the main difference between real ales and craft beers is not the production process, but simply the method of serving.
Does this make a difference? This is a controversial question even within CAMRA, and the answer is that it's a matter of opinion. In the spirit of experimentation, I have tried some craft beers: I've quite enjoyed them, and found they were far superior to old-style keg beers. However, to me they were very like bottled beers, which can be very enjoyable but do not match my personal first choice: draught real ale. Why not go out and have fun deciding what you prefer?