In 1993, [Steven M.] Greer founded the Disclosure Project, the goal of which is to publicly disclose the government’s alleged knowledge of UFOs, extraterrestrial intelligence, and advanced energy and propulsion systems.
https://github.com/davepinch/pinchy.cc/blob/master/content/topics/ufology/disclosure-project/disclosure-project.md
The derivative of a function of a single variable at a chosen input value, when it exists, is the slope of the tangent line to the graph of the function at that point.