What is a knowledge graph?
A knowledge graph is a model that acquires and integrates information from many sources, categorises that data into a framework — what kinds of things there are, what properties they carry, how they relate — and applies a reasoner to it. The reasoner is an application that uses the framework to derive facts about a system from its current state: facts that were never written down anywhere in the graph.
The definition is Lisa Ehrlinger and Wolfram Wöß's. The three verbs are the whole of it.