tagset is a list of part-of-speech tags (POS tags for short), i.e. labels used to indicate the part of speech and sometimes also other grammatical categories (case, tense etc.) of each token in a text corpus.

Stanford Arabic parser tagset is available in Arabic corpora annotated by the tool Stanford parser that was developed by the Stanford NLP group at Stanford University.

An Example of a tag in the CQL concordance search box: [tag=”VBD”] finds all verb past tenses, e.g. كان

Tagset summary

Basic notation

noun (DT)?NN.*
verb VB.*
adjective (DT)?JJ.*
adverb W?RB
conjunction CC
preposition IN
punctuation PUNC

Complete notation

Source: http://nlp.stanford.edu/software/parser-arabic-faq.shtml#d