A business structure in which an individual and his/her company are considered a Single entity for Tax and Liability purposes. A Proprietorship is a company which is not registered with the state as a limited Liability company or corporation. The owner does not pay income Tax separately for the company, but he/she reports business income or losses on his/her individual income tax Return. The owner is inseparable from the proprietorship, so he/she is Liable for any business Debt. also called Sole proprietorship.