If you own your business or do freelance work, you're self-employed. Self-employed people don't work for an employer.
When someone is employed, it means they work or have a job. When you're self-employed, you work and pay income taxes like any other worker, but the way your job is defined is different. You're either a business owner, or someone who does freelance jobs. You might be a self-employed plumber or a self-employed editor — either way, you work for yourself.