In the world of web browsing small packets of information called “cookies” are used to catalog important information used from login passwords and usernames to the items in your online shopping carts.
However these little packets of information aren’t always used for such necessary web functions. Corperations can add, through their own on site ads, third party cookies that can be used to gather information on what webpage you have just visited.
Invasive as it may seem the purpose is simply focusing their advertisments more directly at you.
Most modern web browsers that are worth their salt have a feature that lets you to select which cookies you would like to accept. For example Mozilla’s Firefox has a check box for accepting cookies and a nother one for accepting third party cookies, unchecking the third party cookies box will deny access to your computer for applications/pop-ups that are not part of the site you are currently visiting. Likewise Apple’s Safari browser has three radio buttons for accepting cookies; “Always”, “Never”, and “Only from sites I visit” (in fine print below: “Block cookies from third parties and advertisers”.)