Visual programming or visual scripting is a way to program things with visual nodes. By placing nodes and linking them one can make the program perform the desired action. It is useful for level designers and mission scripters that do not feel like learning all the details of a programming language.
Nodes
Connections
Graph
Reference
Tools for the Job, Part 1: The Nodegraph System - 2016
Unreal: Blueprints Visual Scripting
Stingray: Visual programming using Flow