In The Telegraph, the Thinking Drinkers have a nice profile of gin:
According to EU legislation, gin is made from 96% highly rectified spirit and must ‘taste predominantly of juniper’. Taste is subjective so the assertiveness of juniper aroma and flavour is a talking point in the purists’ debate. It must also have a minimum of 37.5% abv, and at its most basic, gin can include flavourings.