A firm is a business entity that sells goods or services to make a profit. It can be a company such as a corporation, limited liability company, or partnership. The term "firm" is often used interchangeably with "company," but it typically refers to a for-profit business managed by two or more partners providing professional services, such as a law firm. A firm can also describe service providers such as barbers. The theory of the firm posits that firms exist to maximize profits. There are four primary types of firms: sole proprietorship, partnership, limited liability company, and corporation. Legal and accounting firms are often organized as partnerships. A firm can be any size, and it is distinguished primarily by its source of revenue and not by how it is organized.