A layer seven firewall designed to block threats at the application layer of the open system interconnection model, the OSI model. 

CyberWire Glossary link: https://thecyberwire.com/glossary/web-application-firewall

Audio reference link: “VCF East 9.1 - Ches' Computer Security Adventures - Bill Cheswick.” YouTube, 29 Dec. 2015, https://youtu.be/trR1cuBtcPs.