A cookie that remains on a computer because it is stored on the hard disk as a text file rather than stored in the temporary cache file of the browser. It’s sometimes stored in the browser preference folder. Persistent cookies can be configured to last for extended periods of time and the site that places them can track them for days, weeks, months and even years, so long as the text file is not deleted from the hard drive.
 
In contrast, a non-persistent cookie is not stored on the hard drive of a computer and as such will be cleared when you close your browser or turn off your computer.
 
Note: It's important to mention that cookies cannot give out personal information stored on your hard drive. For example, if you have electronically registered a piece of software (like MS Word) with your name, address and telephone number, a cookie cannot extract this information and send it back to the site that placed it. Also, persistent cookies are required in affiliate marketing because an affiliate’s income depends on receiving the credits (that cookies provide) for referring sales or traffic to other web sites.