Natural language processing is a discipline used to facilitate the human/machine interface, ultimately to make it easier for people to ‘talk’ to machines and understand what the machine is saying when it replies. It works by recognising words, phrases and grammar rules and extracting the meaning therein.
The particular AI system that achieved this result was the Conceptnet semantic network. Researchers from the University of Chicago ran a test based on the verbal part of the Wechsler Preschool and Primary Scale of Intelligence applied against the ConceptNet4 system. The result was that the natural language processing system matches the verbal IQ of a four year old human child.
The full report is freely available online at this link.