Caching – The practice of temporarily storing files on local servers for quick retrieval the next time the file is needed. Cached files supply an old copy that may not be up to date with the file stored at the original source, but are often necessary for improving page load performance.

Campaign – The advertising period in which an ad delivery strategy is executed.
CDN An acronym for Content Distribution Network, a CDN is a system of geographically dispersed servers used to provide web content to a browser or other client. Files are strategically pulled from a server on the network based on the location of the user, the requesting server, and the delivery server of the CDN to provide the best delivery performance.

CLEAR Ad Notice – CLEAR is an acronym for “Control Links for Education and Advertising Responsibly,” a set of technical guidelines developed by the Interactive Advertising Bureau (IAB) and the Network Advertising Initiative (NAI) to empower members of the online advertising community to communicate their presence and behavioral advertising targeting practices (if any) to consumers in a simple and direct manner. Derived from: http://www.iab.com/media/file/CLEAR_Ad_Notice_Final_20100408.pdf

Click – An interaction between a website visitor and the browser in which the website visitor uses a device, such as a mouse, to move the cursor (or pointer) to an active area of the screen and then deliberately interacts with that area by clicking a button on their device, triggering an event. In the case of touch-screen devices, the user “clicks” by touching the active area with their finger or a stylus.

Close X – A creative control that enables a user to close an ad (remove it from view) or to reduce an expanded panel back to its original size.

Collapse – An event where the expanded panel of an expandable ad reduces to its original size, or disappears completely.

Compression – The practice of packaging a digital file so that it uses less storage space.

Controls – Active elements of an ad that enable a user to control the advertising experience. Examples of common controls include the “Close X” button in an expandable ad or the Play/Pause/Mute buttons in a video player.

CPU – CPU is an acronym for Central Processing Unit, the key component of a computer system, which contains the circuitry necessary to interpret and execute program instructions.

CPU Usage % – A guideline for the amount of central processing power used to display advertising content compared to what’s available on an individual’s computer. CPU usage percentage can be measured directly, during the execution of an online ad. In addition to file size, the complexity of drawings, gradients, slow moving animations and detailed moving elements can affect the number of calculations the CPU must make for each frame.

CPU Spike – A brief increase in central processing power, sustained for no more than a few seconds, experienced while “heavy” content is loaded/executed.

Creative – An advertising unit created by an ad designer, in accordance with publisher specifications and guidelines, for the purpose of communicating a marketing message to that publisher’s audience. One creative may consist of multiple files in various formats, such as standard images, animation, video, execution files (.html, .js, etc.) and other files that work together for an interactive experience.

Creative Dimensions – Measured in pixels, the width and height of an ad unit (WxH). The width is always the first dimension listed, followed by the height dimension (i.e. an ad that is 300×250 is 300 pixels wide by 250 pixels high).
Cursor – The graphical representation of a “pointer” on a user screen, controlled by the user’s interaction with controlling devices such as a mouse, mouse pad, stylus or other input hardware.