# Additional industry definitions + **Beacon:** Tracking pixels or tags that are used to measure ad performance, attribution, and analytics. + **Click:** A metric that is counted every time someone clicks on an ad, even if the person doesn't reach the website (such as when it's temporarily unavailable). + **Fill rate:** Ad impressions generated in the ad space divided by the total inventory available on that ad space. + **Impression:** An ad view is counted every time a creative (ad) is served to a user. The impression is considered one of the basic campaign performance indicators. + **Industry advertising bureau (IAB):** An advertising business organization that develops industry standards, conducts research, and provides legal support for the online advertising industry. + **OpenRTB:** OpenRTB is a standard of communication between buyers and sellers of real-time bidding (RTB) advertising, allowing advertising platforms (demand-side platforms, supply-side platforms, and ad exchanges) to speak the same language when conducting online media transactions.  + **Real-time bidding (RTB):** The process of purchasing and selling digital ad space through real-time auctions that occur in the time it takes a webpage to load  + **Programmatic advertising:** The buying and selling of online media via automated systems (advertising platforms). + **VAST (video ad-serving template):** An XML schema developed by the IAB that allows in-stream video ads to be served from video ad servers and played in video players across a number of websites, or publishers, and on numerous devices (for example, desktop computers, mobile devices, or tablets).