"To watch an ad" means to view or look at a promotional video or commercial that is meant to persuade people to buy a product or service. Full definition
You can try it for free and then pay for the levels that you want, or unlock them using gems by watching ads. (droidgamers.com)
An increase in Stories usage would definitely help, and Snap could mitigate a possible ad revenue decline by forcing users to watch an ad for at least three seconds before skipping. (androidauthority.com)
Even when viewers fast - forward, at least one study shows that they're just as aware of which brands are being advertised as those who watch the ads in their entirety. (epolitics.com)