A small business may be defined as a business with a small number of employees. The legal definition of "small" often varies by country and industry, but is generally under 100 employees in the United States while under 50 employees in the European Union (In comparison, the American definition of mid-sized business by the number of employees is generally under 500 while 250 is for that of European Union). These businesses are normally privately owned corporations, partnerships, or sole proprietorships.

However, other methods are also used to classify small companies, such us annual sales (turnover), assets value or net profit (balance sheet), alone or in a mixed definition. These criteria are followed by the European Union, for instance (headcount, turnover and balance sheet totals).

Small businesses are common in many countries, depending on the economic system in operation. Typical examples include: convenience stores, other small shops (such as a bakery or delicatessen), hairdressers, tradesmen, solicitors, lawyers, accountants, restaurants, guest houses, photographers, small-scale manufacturing etc. Small businesses are usually independent.

The smallest businesses, often located in private homes, are called microbusinesses (term used by international organizations such as the World Bank and the International Finance Corporation) or SoHos. The term "mom and pop business" is a common colloquial expression for a single-family operated business with few (or no) employees other than the owners. When judged by the number of employees, the American and the European definitions are the same: under 10 employees.