See this simple introduction to Natural Language Processing (NLP)

The most basic and well known application of NLP is Microsoft Word spell checking. Text analysis, also known as sentiment analytics is a key use of NLP. Businesses are most concerned with comprehending how their customers feel emotionally and use that data for betterment of their service. Email filters are another important application of NLP. By analyzing the emails that flow through the servers, email providers can calculate the likelihood that an email is spam based its content by using Bayesian or Naive based spam filtering.