Text chunking consists of dividing a text in syntactically correlated parts of words, like noun groups, verb groups, but does not specify their internal structure, nor their role in the main sentence.
Parts are tagged according to the conventions of the Penn Treebank Project (http://www.cis.upenn.edu/~treebank/). For example, a plural noun is denoted NNS, a singular or mass noun is NN, and a determiner (such as a/an, every, no, the,another, any, some, each, etc.) as DT.
For more information visit http://opennlp.apache.org.