Tagging:  The descriptors are called the tags and theautomatic assignment of the descriptors to the given tokens is called tagging.POS TaggingThe process of assigning one of the parts ofspeech to the given word is called Parts Of Speech tagging, commonly referredto as POS tagging. Parts of speech include nouns, verbs, adverbs, adjectives,pronouns, conjunction and their sub-categoriesPOS TaggerA Part-Of-SpeechTagger (POS Tagger) is a  software thatreads text and then assigns parts of speech to each word (and other token),such as noun, verb, adjective, etc., It uses different kinds of informationsuch as dictionary, lexicons, rules, etc.

because  dictionarieshave category or categories of a particular word, that is a word may belong tomore than one category. For example, run is both noun and verb so to solve thisambiguity taggers use probabilistic information.There are mainlytwo type of taggers: Rule-based – Useshand-written rules to distinguish the tag ambiguity. Stochastictaggers are either HMM based – chooses the tag sequence which maximizes theproduct of word likelihood and tag sequence probability, or cue-based, usingdecision trees or maximum entropy models to combine probabilistic features.