出售 (chū shòu) is a formal verb meaning 'to sell' or 'to offer for sale', used in written notices, business contexts, or for selling property/goods. It is more formal than the everyday word 卖 (mài, HSK1) and similar in register to 销售 (xiāo shòu, HSK5), though 销售 often implies marketing or selling as a business activity.