The Flux Advanced Security Kernel (FLASK) is an operating system security architecture that provides flexible support for security policies. It is a joint venture between the National Security Agency, the University of Utah, and the Secure Computing Corporation project designed to provide a framework for a more secure operating system. Development and implementation started with the Mach microkernel, and has since shifted its focus to the Linux operating system. It is now better known as Security-Enhanced Linux (or SE Linux). FLASK is a core framework in security-focused operating systems such as NSA's Security-Enhanced Linux (SELinux), OpenSolaris FMAC and TrustedBSD. This means that SELinux can be thought of as an implementation of FLASK.

Flask may refer to:

• Laboratory flask, laboratory glassware for holding larger volumes than simple test tubes
  • Erlenmeyer flask, a widely used type of laboratory flask which features a flat bottom, a conical body, and a cylindrical neck
• Vacuum flask a container designed to keep warm drinks warm and refrigerated drinks cold
• Hip flask, a small container used to carry a small amount of liquid
• Flask (casting) a container without a top or bottom, with sides only, used to hold molding sand
• Flask (web framework) a web framework for the Python programming language
• Powder flask
• FLASK, the Flux Advanced Security Kernel, an operating system security architecture
• Flask, a 76-pound (34.46 kg) unit of mass used to measure mercury. Mercury does not react with iron. Historically, mercury was stored and shipped in iron flasks.