An S corporation (also referred to as an S corp) is a special type of corporation created through an IRS tax election. An eligible domestic corporation can avoid double taxation (once to the corporation and again to the shareholders) by electing to be treated as an S corporation.
An S corp is a corporation with the Sub-chapter S designation from the IRS. What makes the S corp different from a traditional corporation (C corp) is that profits and losses can pass through to your personal tax return. Consequently, the business is not taxed itself. Only the shareholders are taxed. There is an important caveat, however: any shareholder who works for the company must pay him or herself "reasonable compensation." Basically, the shareholder must be paid fair market value, or the IRS might reclassify any additional corporate earnings as "wages."