An ale is a beer that has been fermented using a top fermenting yeast. Ale yeasts are typically more resilient to warmer temperatures then their lager counterparts and are usually fermented at a temperature range of 65-75 F. Since the yeast is more active at higher temperatures, an ale ferments much quicker then a lager.
Examples of ales include golden ales, pale ales, India pale ale, old ale, Belgian ale and barley wines.
Something to keep in mind when fermenting an ale is that ale yeast can ferment beer above a temperature of 75 F, but when doing so it will oftentimes create undesirable esters and off flavors. Also, liquid ale yeast is vulnerable to high temperature, and it should be refrigerated to maintain its viability in transit and in storage. Due to the delicate nature of liquid yeast, I always create a yeast starter to verify its viability prior to pitching it in the cooled wort.