The ads that are placed within the social network Facebook are called Facebook Ads.
In contrast to Google Ads, the ads are not displayed to the user based on a search query, but on the basis of the user's interests and preferences that he or she has disclosed on Facebook (e.g. favourite music, relationship status, place of residence, etc.) or his or her surfing behaviour on websites that use the Facebook Pixel, thus reducing scattering losses for the advertiser.
The Facebook Pixel is necessary to run retargeting and lookalike campaigns.