Natural Language Processing
Natural Language Processing is a subcategory of AI, but also a "school of thought" about how AI should be properly done.

More commonly, NLP refers to a set of algorithms, theories and techniques used to process natural language (that spoken by humans) on computers. There is a huge variety of techniques, mostly emerging from the forty year tradition of grammatical linguistics, that allow for part of speech identification, phrase-identity and various means of converting labelled text sequences or parse trees into some semantic formulation.

Subset of natural language processing can be used for various applications such as in the Information Retrieval and Question Answering community which looks over large corpora for patterns which indicate semantic relations (without actually understanding the text itself). Natural language used as a command and control interface can also be done with the basic tools that are available for identifying parts of speech and specific lexical terms.