To ensure private data protection, information about users is stored in cookies.
"A cookie is a small piece of data that a website asks your browser to store on your computer or mobile device. The cookie allows the website to "remember" your actions or preferences over time."
European Commission website
"Cookies are generally divided into essential and non-essential. The essential cookies are those necessary for providing the information requested by the user. All the other cookies are considered non-essential. Included here are identifiers used for analytics, cookies from advertisers or third parties, including affiliates and those that identify a user when he returns to the website. The EU cookie law is meant to target the non-essential category."
EU GDPR Compliant website