Businesses fall under one of two federal tax systems:

Taxation of both the entity itself (on the income it earns) and the owners (on dividends or other profit participation the owners receive from the business). This system applies to the business S-corporation-called the "C-corporation" (C-corp) for reasons we'll see shortly-and the system of taxing first the corporation and then its owners is called the "corporate double tax."
"Pass through" taxation. The entity (called a "flow-through" entity) is not taxed but its owners are each taxed (more or less) on their proportionate shares of the entity's income. The leading forms of pass through entity (further explained below) are:
Partnerships, of various types.
"S-corporations" (S-corps), as distinguished from C-corps.
Limited liability companies (LLCs).
A sole proprietorship such as John Doe Plumbing or Marcus Welby, M.D. is also considered a pass through entity even though no "organization" may be involved.
The first major consideration (in this case, a tax consideration) in choosing the form of doing business is whether to choose an entity (such as a C-corp) that has two levels of tax on income or a pass through entity that has only one level (directly on the owners).
Losses are directly deductible by pass through owners while C-corp losses are deducted only against profits (past or future) and don't pass through to owners. The major business consideration (as opposed to tax consideration) in choosing the form of business is limitation of liability, that is, to protect your assets from the claims of business creditors. State law grants limitation of liability to corporations (C and S-corps), LLCs, and partners in certain forms of partnership. Liability for corporations and LLCs is generally limited to your actual or promised investment in the business.

Different Types of Business Entities
C and S-Corps
The S-Corp