A remarketing target is created when you apply a Google Ads remarketing list to a Google Ads manual campaign, Shopping campaign, or ad group.
A campaign or ad group remarketing target is used to display different ads or to bid differently to reach customers who have previously visited your site.
If you don't know how much to bid to reach those customers, you can apply bid strategy or conversion goal to the campaign to automatically set or recommend remarketing target bid adjustments.
A Google Ads remarketing list can be applied to a Google Ads campaign or ad group for negative remarketing as well. That is, to exclude the members of list from receiving additional ads.