事儿 is the erhua (儿化) variant of 事 (shì), commonly used in Northern Mandarin. It means 'matter', 'affair', or 'business', and in colloquial speech can also refer to 'trouble' or 'problem'. In the phrase 事儿多 (shìr duō), it describes someone who is fussy, demanding, or hard to please — a common conversational usage. As a noun, it pairs with classifiers 件 (jiàn) and 桩 (zhuāng).