The definition of a first party-cookie is the website providers’ own cookie. Meaning that this cookie is put on the user’s device directly by the website the user is visiting. The used website creates the cookie when the user visits it. By default, web browsers generally allow first-party cookies. This is because they help you move from one page to another on the same website.
For example, you cannot add items to your basket when shopping online without using first-party cookie. Every additional item would, because of the disabled first-party cookies, result in the set-up of a new order. Another term for first-party cookies is functional cookies.