Two common definitions:- In the UK/Europe, refers to inventories or finished goods held by a company to satisfy the immediate requirements of customers. In USA, refers to Shares and other investment assets in Corporations, e.g. Ordinary shares are called 'Common Stock' - remember the old term 'Stocks and Shares'.
If you are European - it's the stock in trade of finished goods that you need to instantly satisfy the customer's demands. If you are American, it's the term for 'Stocks and Shares' or 'Common Stock' - the shares that are bought and sold on the NYSE.