Many words are habitually put together - or collocated. A collocation is any habitually linked group of words - a kind of lexical partnership, e.g. 'fish and chips', 'salt and pepper', 'don't mention it', 'it's nothing...', 'Oh well!', 'bangers and mash'... and so on. Many idioms or idiomatic phrases exhibit collocation, e.g. in a jiffy.