When the linking of several ad tags usually from different exchanges ad servers or ad networks creates a ''waterfall'' – or ''daisy chain'' – of impressions passing from tag to tag. If no creative is found via the demand available to Ad Tag 1 the impression can be passed to Ad Tag 2 Ad Tag 3 and Ad Tag 4 to see if demand is available there and so on until a creative is found and served.

The Digital Advertising Alliance. An online advertising industry association made up of many other organizations and dedicated to self-regulation. Possibly best known for the Advertising Option Icon. Read more on the DAA's website.

Click-through rate - literally the rate or frequency at which users click through to a landing page from an ad.

Comma separated values. A data file structured in a table form with fields separated by commas. This is one file format used to transmit multiple creative tags during bulk sending.

Similar to an ad tag this is a snippet of code that gives the location of the creative which is usually a content delivery network (CDN) or an ad server.

The actual graphical advertisement itself. Common creative formats include GIF JPEG JavaScript HTML and Flash.

Cost per mille or thousand viewable impressions (mille = thousand in Latin). A pricing model in which advertisers pay for every 1000 viewable impressions of their advertisement served. Viewability refers to whether an impression was actually seen by the user and can be determined according to a variety of methods.

Cost per mille or thousand (mille = thousand in Latin). A pricing model in which advertisers pay for every 1000 impressions of their advertisement served. This is the standard basic pricing model for online advertising. See also CPC and CPA.

Cost per install. A payment model in which mobile advertisers pay each time a user installs their app.

Cost per Completed View; the price paid by an advertiser to the publisher once a video has been viewed through completion.

Cost per click. A payment model in which advertisers pay each time a user clicks on their advertisement.

Cost per action/acquisition. A payment model in which advertisers pay for every action such as a sale or registration completed as a result of a visitor clicking on their advertisement. Note that an ''acquisition'' is the same as a ''conversion''.

A payment model in which advertisers agree to pay the cost of media plus an additional CPM or % profit margin on top.

A parcel of text sent by a server to the cookie file in a browser and then sent back unchanged by the client each time it accesses that server. HTTP cookies are used for authenticating session tracking and storing information about specific users such as site preferences or buying habits. Advertisers often use cookies to track the number and frequency of advertisements that have been shown. See also first-party cookies and third-party cookies.

A pixel that fires when a user ''converts'' by clicking on a ad registering making a purchase or completing another action. Advertisers can place conversion pixels on a landing page registration page checkout pages or elsewhere to track conversions.