Definition
The form attached to Form 1040 where sole proprietors, freelancers and many creators report business income and expenses to find their profit or loss.
What it means
Schedule C (Form 1040), Profit or Loss From Business, is used by people who run a business as a sole proprietor or single-member LLC, including freelancers, gig workers and creators who earn from ads, sponsorships or sales. Part I lists gross receipts; Part II lists expenses by line, such as advertising, contract labor, office expense, supplies, travel and business meals, with other expenses listed in Part V. The net profit flows to Form 1040 and is also used to figure self-employment tax on Schedule SE. A net loss may reduce other income if the activity is a business rather than a hobby. Keeping records by Schedule C category through the year makes filing easier.
Example
A YouTuber with $30,000 of income and $8,000 of expenses reports a $22,000 net profit on Schedule C, which is the base for her income tax and self-employment tax on that business.
Illustrative numbers only. Your situation will differ.