Stocks or shares are terms that are used to represent units of ownership in a company. When you purchase stocks or shares of a company, you become one of the owners of that company. For instance, if a company issues 100 shares and you purchase 50 shares, you're said to hold 50% ownership of that company.
Being a shareholder and a part-owner of a company gives you certain rights and privileges. This includes the right to vote on company matters and the opportunity to receive a part of the profits generated by it by way of dividends.