The LLC - or Limited Liability Company - is the newest form of business incorporation, and is often described as a combination of a corporation and a partnership.
An S corporation is a special type of corporation that draws its designation from Subsection S of the tax code. To start an S corporation, a small business owner starts a C corporation, then files for S corporation status with the IRS.
A C corporation - often just called a generic corporation - is the oldest and one of the most common business entities. A C corporation is a completely separate tax and legal entity from its owners.
A nonprofit corporation is a corporation whose principal purpose is public benefit. It provides a shield against potential liability for its directors, officers and employees.