A Sole Proprietor is a business that is not seperate from it's owner. The owner pays the business taxes on their personal return and is fully liable for all debts.

A Partnership is owned by two or more persons. There are several types of Partnerships which have differing levels of liability. The partners report their share of the business income on their personal return.

A corporation is an entity unto itself, a person under law. The owners are the shareholders that elect a board of directors who selects the executives to manage the day to day business. The shareholders are not liable for the debts of the Corporation. There are different types of Corporations. 

An LLC, Limited Liability Company, is a hybrid entity possessing characteristics of other entities. The LLC is owned by its members who are not liable for the business debts. An LLC can choose to be taxed like other entities.