A tiny snippet of data that gets added to the user’s web browser when they visit a certain website. The code is stored in the user’s browser over a period of time set by creators. Cookies are used for:
• Retargeting ads to users
• Storing stateful data like shopping cart items
• Autocompleting forms
• Authentication details for user log-ins and accounts.
See "Site Retargeting". https://www.targetinternet.com/digital-marketing-guide-to-cookies/