Definition
If you earn a commission when people buy through your links, the FTC expects you to say so clearly near the link or recommendation.
What it means
An affiliate link pays the person who shares it a commission when someone buys after clicking it. The FTC treats that commission as a material connection that readers or viewers may not expect, so it must be disclosed clearly and close to the recommendation, not only on a separate page or at the bottom of a long post. A short statement such as "I earn a commission if you buy through these links" works when people can see it before they click. In videos, it should be said as well as shown. Affiliate programs often add their own rules; Amazon, for example, requires its Associates to use a specific disclosure statement. Affiliate commissions are also taxable income.
Example
A tech blogger places "I may earn a commission from links on this page" right above a list of recommended laptops, not only in the site's footer.
Illustrative numbers only. Your situation will differ.