Small businesses are types of corporations, partnerships, or sole proprietorships which have a small number of employees and/or less annual revenue than a regular-sized business or corporation. Businesses are defined as "small" in terms of being able to apply for government support and qualify for preferential tax policy. The qualifications vary depending on the country and industry. Small businesses range from fifteen employees under the Australian Fair Work Act 2009, fifty employees according to the definition used by the European Union, and fewer than five hundred employees to qualify for many U.S. Small Business Administration programs. While small businesses can also be classified according to other methods, such as annual revenues, shipments, sales, assets, annual gross, net revenue, net profits, the number of employees is one of the most widely used measures.

Small businesses in many countries include service or retail operations such as convenience stores, small grocery stores, bakeries or delicatessens, hairdressers or tradespeople (e.g., carpenters, electricians), restaurants, motels, photographers, very small-scale manufacturing, and Internet-related businesses such as web design and computer programming. Some professionals operate as small businesses, such as lawyers, accountants, dentists, medical doctors and developers (although these professionals can also work for large organizations or companies). Small businesses vary a great deal in terms of size, revenues, and regulatory authorization, both within a country and from country to country. Some small businesses, such as a home accounting business, may only require a business license. On the other hand, other small businesses, such as day cares, retirement homes, and restaurants serving liquor are more heavily regulated and may require inspection and certification from various government authorities.