Under IRS standards, a self-employed person is one who engages in business as an independent contractor or sole proprietor or who is a member of a business partnership. Even very casual, part-time business activity constitutes self-employment.
Sole proprietors need not operate a registered business or have a Federal Tax Identification Number from the IRS to be considered self-employed. A person who holds a full-time job and independently sells a service on the weekends, for example, is both an employee and a self-employed person. Whenever a person is in business for oneself, the income earned as a result of that business activity is considered self-employment income. Self-employment income is subject to taxation according to IRS regulations.