Self employment tax is the equivalent of social security and Medicare tax. In fact it is paid at the same rates and with the same limits.
People who have their own business, work as independent contractors, or are
partners in partnerships (or LLCs) are subject to this tax. The biggest
difference between it and social security tax as an employee is that the self
employed person pays both halves of the tax where in an employment relationship
one half is paid by the employee and one half by the employer.