A collocation is a combination of words that naturally go together, like "fast food" or "quick shower", as opposed to unnatural combinations. There are several types of collocations including adjective-noun, verb-noun, and adverb-adjective combinations. Learning collocations can make your language more natural and help you express yourself in a richer way, as our brains process language in chunks rather than single words. It is important to learn collocations, notice them when reading, and practice using them.