Like many beer styles, pale ale resulted from an innovation in brewing technology. The brewers in Burton-on-Trent in England were looking for a way to produce a more consistent and paler beer. The kilns of the day used wood which was difficult to control and often resulted in dark roasted or even scorched barley. They found that coke, a processed form of coal that burns hot and steady, gave them the desired effect - a clear, amber or copper colored ale. It was far paler than any British ales brewed to date.
The type of water used seems to be more sacred to this style than anything else. Brewers all over the world that make this style often work hard to reproduce the naturally occurring water of the original brewery in Burton. They will use hops and yeast that are completely different from those used in traditional English ales but they will bend over backwards chemically treat their water until it is as hard as Burton-on-Trent's.
Naturally, pale malt is used to make pale ale. British varieties can have a bit of crystal but typically no more than 20% and no darker than 20-40 SRM. The hops chosen traditionally include Fuggles, Kent Goldings and Northern Brewer with Cascades, Mt. Hood and other local varieties showing up in American brews. This continues to be a style that is pretty forgiving of innovation.
The traditional British pale ale style, which includes bitter and ESB, is a very pleasant and understated beer. It has a malty profile and just enough woody or lightly floral hops for balancing. It is elegant and a great session beer. The American and Australia version of this very mutable style are brasher. The maltiness is often dialed down and more aggressive hops varieties are used making it an exciting and spicy brew.
There is such a wide range of interpretations of pale ale, it is hard to say which foods pair well with it. British pale ales tend to be maltier in flavor and less hoppy so they can be enjoyed with a wider variety of foods including spicy dishes from India and Asia. They are also good with the blander dishes of the UK. Pale ales brewed outside of England, especially those from America, tend to be hoppier with less malt flavor so they go best with simpler dishes such as grilled meat.