An HTTP cookie (also called web cookie, Internet cookie, browser cookie, or simply cookie) is a small piece of data sent from a website and stored on the user's computer by the user's web browser while the user is browsing.

SameSite Cookies has a very insightful article on SameSite cookies. Read it to understand how they work.

Value Intended Use Example
SameSite=Lax Functionality affecting the display of the site. Includes first request. Theme switcher
SameSite=Strict Relating to actions the user initiates. From second request. Password change
SameSite=None Functionality affecting the embedding of the site content.
Cookies with SameSite=None must also specify Secure, meaning they require a secure context.
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- Legacy.
Cookies without a SameSite attribute will be treated as SameSite=Lax.