K4 is the K programming language, Q is a language built on top of K. They are the practical over achieving members of the array family of programming languages.

shoutout to bryan @bcantrill who I think explained K best at https://youtu.be/2wZ1pCpJUIM?si=y4ugbFXroTZc22AY&t=471 and https://queue.acm.org/detail.cfm?id=1531242