As described in the definition document by the ietf:
https://tools.ietf.org/html/draft-west-first-party-cookies-07

"The 'SameSite' attribute allows servers to assert that a cookie
ought not to be sent along with cross-site requests. This assertion
allows user agents to mitigate the risk of cross-origin information
leakage, and provides some protection against cross-site request
forgery attacks."