S -> Simple declarative clause, i.e. one that is not introduced by a
(possible empty) subordinating
conjunction or a wh-word and that does not exhibit subject-verb
inversion.
SBAR -> Clause introduced by a (possibly empty) subordinating conjunction.
SBARQ -> Direct question introduced by a wh-word or a wh-phrase.
Indirect questions and relative clauses should be bracketed as
SBAR, not SBARQ.
SINV -> Inverted declarative sentence, i.e. one in which the subject
follows the tensed verb or modal.
SQ -> Inverted yes/no question, or main clause of a wh-question, following
the wh-phrase in SBARQ.
ADJP -> Adjective Phrase.
ADVP -> Adverb Phrase.
CONJP -> Conjunction Phrase.
FRAG -> Fragment.
INTJ -> Interjection. Corresponds approximately to the part-of-speech tag
UH.
LST -> List marker. Includes surrounding punctuation.
NAC -> Not a Constituent; used to show the scope of certain prenominal
modifiers within an NP.
NP -> Noun Phrase.
NX -> Used within certain complex NPs to mark the head of the NP.
Corresponds very roughly to N-bar
PP -> Prepositional Phrase.
PRN -> Parenthetical.
PRT -> Particle. Category for words that should be tagged RP.
QP -> Quantifier Phrase (i.e. complex measure/amount phrase); used within
NP.
RRC -> Reduced Relative Clause.
UCP -> Unlike Coordinated Phrase.
VP -> Verb Phrase.
WHADJP -> Wh-adjective Phrase. Adjectival phrase containing a wh-adverb, as
in how hot.
WHAVP -> Wh-adverb Phrase. Introduces a clause with an NP gap. May be null
(containing the 0 complementizer)
or lexical, containing a wh-adverb such as how or why.
WHNP -> Wh-noun Phrase. Introduces a clause with an NP gap. May be null
(containing the 0 complementizer)
or lexical, containing some wh-word, e.g. who, which book, whose
daughter, none of which, or how
many leopards.
WHPP -> Wh-prepositional Phrase. Prepositional phrase containing a wh-noun
phrase
(such as of which or by whose authority) that either introduces a
PP gap or is contained by a WHNP.
X -> Unknown, uncertain, or unbracketable. X is often used for bracketing
typos and in bracketing
the...the-constructions.
Credit: http://mail-archives.apache.org/mod_mbox/opennlp-users/201402.mbox/%3CCACQuOSXOeyw2O-AZtW3m=iABo1=3cpZOdPiWFXoNwN-SVWo4gQ@mail.gmail.com%3E