'Summat' means 'something'. It is not standard English — it is a dialect word, most strongly connected with the north of England (Yorkshire, Lancashire, the Midlands). When you hear it, you are hearing a person's region and often their background, not a mistake. It works in a sentence exactly where 'something' would: 'There's summat wrong with the car.' 'Say summat!' 'He's got summat to tell you.' Sometimes it also carries the older feel of 'somewhat', a little bit: 'She looked summat tired.' That use is rarer today. You will meet this word mostly in three places: in speech in the north, in novels and TV dramas where a writer wants a character to sound northern, and in fixed sayings like 'there's nowt so queer as folk' territory, where 'nowt' (nothing) and 'summat' travel together. Learners should read it and understand it, but should not use it themselves unless they live in that part of England — spoken by an outsider it sounds like an imitation rather than a natural voice. Note also that in Britain, dialect words like this are heard as warm and homely by some people and as 'uneducated' by others; that judgement is about class and prejudice, not about the word.

「某物、某事」的英格蘭北方方言說法，等於 something；文學或影視裡用來標示說話者的北方口音