A payment made by a company (or a fund holding that company's shares) to its shareholders, usually drawn from profit, distributed on a regular schedule — monthly, quarterly, or annually.
Some companies, once they're profitable and stable, choose to share a portion of that profit directly with the people who own their stock, rather than reinvesting every dollar back into the business. If you own shares (directly, or through an ETF that holds them), you get a small cash payment — typically every three months — for as long as you hold those shares, on top of whatever the share price itself does.
If a stock pays a $1 annual dividend and you own 100 shares, you'd receive roughly $100 a year in dividend payments — usually split into 4 quarterly payments of $25, or 12 monthly payments if the company pays monthly — regardless of whether the stock price went up or down that year.