Cookies
A cookie is a file that is stored on the client's machine.
Cookies are written by domains to store information on the client's machine.
Domain specific
Cookies are only sent by the browser to the domain which wrote them.
With every request to a specific domain, the client's web browser looks to see if there is a cookie from that domain on the client's machine. If there is a cookie that has been written by that particular domain, then the browser will send the cookie with every request to that domain.
Cookies are domain specific.
Limits
We can store whatever information we would like in a cookie up to a certain size limit. The size limit of a cookie is dependent upon the browser but is usually around 4096 characters.
There is also a limit to the number of cookies one domain can write. This limit is also browser specific.
See this resource for more information.
Expiring a cookie
If the Expires or MaxAge field isn't set, then the cookie is deleted when the browser is closed. This is colloquially known as a "session cookie."
You can expire a cookie by setting one of these two fields: Expires or MaxAge
Expires sets the exact time when the cookie expires. Expires is Deprecated.
MaxAge sets how long the cookie should live (in seconds).