http://online.wsj.com/article/SB10001424052748703999304575399492916963232.html

JULY 31, 2010

What They Know: A Glossary

Key tracking terminology

Ad exchange -- An auction-based marketplace where advertisers can bid to place ads in the space offered by websites.

Ad network -- A company that sells ads on behalf of website publishers.

Aggregated information -- Data combined from many individual users that can't identify anyone personally.

Anonymous information -- Facts about you that don't identify you personally, such as age group and gender.

Beacons -- Invisible software on many websites (also known as "bugs" or "pixels") that can track web surfers' location and activities online. Some are powerful enough to know what a user types on a particular site.

Behavioral targeting -- Advertisers and websites use information about where you browse and what you search for online to guess your interests and decide what ads to show you. It's also called interest-based advertising or customized ads.

Cookie -- Tiny text file put on your PC by websites or marketing firms that--depending on its purpose--might be used simply to remember your preferences for one site, or to track you across many sites.

Data exchange -- A marketplace where advertisers bid for access to data about customers. Marketers then use this data to target ads. For example: A Denver hotel might bid to reach people known to have researched Denver hotels recently.

Exposure index -- The Journal's analysis of how exposed your data is when you visit a website that has trackers. Each tracker was given a score based on how the tracking company collects, shares, and uses your data. A website's exposure index was calculated using the sum of the scores of all of the trackers we found on that site.

First-party tracking file -- Typically a cookie installed on your computer by a website for benign purposes such as keeping you logged in to that one site.

Flash cookie -- Small file put on your computer by Adobe's Flash software, which is used by many sites to display video or ads. Flash cookies can be designed to re-install regular cookies that were previously deleted.

Internet Protocol (IP) address -- A unique number assigned to every computer connected to the internet. Any website you visit can know your IP address, and through that can often know your general location.

Offline data -- Information about you that comes from sources other than the Internet. It could include your zip code, estimated household income, the cars you own, or the purchases you've made in a store.

Personally identifiable information -- Data identifying you uniquely, such as your name, Social Security number, address or credit-card information.

Privacy policy -- A notice on a website that discloses some or all the ways the site collects or uses information.

Third-party tracking file -- A cookie, beacon or other tracking technology installed on your computer by an ad network or research firm that can track your activities across many websites.

Tracking company -- Companies that use cookies and other tracking technology to collect online data about you.

User profile -- Information about your actions, interests and characteristics that tracking companies compile about you.