Collocation is the linguistic study of words that habitually co-occur — the tendency of certain words to appear together more frequently than chance would predict. Examples: 'make a mistake' (not 'do a mistake'); 'heavy rain' (not 'strong rain'); 'fast food' (not 'quick food'). Collocations are important in language teaching, lexicography, and corpus linguistics. J. R. Firth coined the term, stating 'a word is known by the company it keeps.'