Flavour enhancers are used to bring out the flavour in a wide range of foods without adding a flavour of their own. Extracts, essences, and flavours employing only natural flavouring agents are called pure; those employing synthetics (in part or entirely) are called imitation, artificial or flavourings.
Salt, although not classed as a food additive, is the most widely used flavour enhancer along with Monosodium glutamate (E621) and sweeteners.