Safari 5.1 (OS X Lion): What are cookies?
Cookies can store information that identifies you, such as your name and email address. A website has access only to the information you provide. For example, a website can’t determine your email address unless you provide it. A website can’t gain access to other information on your computer.
Cookies tell a website who you are so that the site can perform a variety of functions that might be convenient for you. The site might store your preferences, such as the type of books you like to read or which movies are of interest to you, or provide tracking information for your online purchases, or remember your scores in an online game you like to play.
By default, Safari accepts cookies only from websites you open. This might help prevent certain advertisers from storing cookies on your computer. You can change your cookies preferences so that Safari blocks all cookies or accepts all cookies.