A 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.

English CLAWS part-of-speech tagset version 2 is available in English corpora annotated by the tool using CLAWS (the Constituent Likelihood Automatic Word-tagging System) developed by University Centre for Computer Corpus Research on Language at Lancaster University.

The Constituent Likelihood Automatic Word-tagging System abbreviated CLAWS was developed by UCREL at Lancaster University. This is the 2nd version of used tagset.

An Example of a tag in the CQL concordance search box: [tag="AT1"] finds all singular articles as a, an, every  (note: please make sure that you use straight double quotation marks)

Tagset

POS Tag Description
! punctuation tag – exclamation mark
$ germanic genitive marker – (‘ or ‘s)
&FO formula
&FW foreign word
( punctuation tag – left bracket
) punctuation tag – right bracket
, punctuation tag – comma
punctuation tag – dash
—– new sentence marker
. punctuation tag – full-stop
punctuation tag – ellipsis
: punctuation tag – colon
; punctuation tag – semi-colon
? punctuation tag – question-mark
punctuation tag – quotation marks
APP$ possessive pronoun, pre-nominal (my, your, our etc.)
AT article (the, no)
AT1 singular article (a, an, every)
BCS before-conjunction (in order (that), even (if etc.))
BTO before-infinitive marker (in order, so as (to))
CC coordinating conjunction (and, or)
CCB coordinating conjunction (but)
CF semi-coordinating conjunction (so, then, yet)
CS subordinating conjunction (if, because, unless)
CSA ‘as’ as a conjunction
CSN ‘than’ as a conjunction
CST ‘that’ as a conjunction
CSW ‘whether’ as a conjunction
DA after-determiner (capable of pronominal function) (such, former, same)
DA1 singular after-determiner (little, much)
DA2 plural after-determiner (few, several, many)
DA2R comparative plural after-determiner (fewer)
DAR comparative after-determiner (more, less)
DAT superlative after-determiner (most, least)
DB before-determiner (capable of pronominal function) (all, half)
DB2 plural before-determiner (capable of pronominal function) (eg. both)
DD determiner (capable of pronominal function) (any, some)
DD1 singular determiner (this, that, another)
DD2 plural determiner (these, those)
DDQ wh-determiner (which, what)
DDQ$ wh-determiner, genitive (whose)
DDQV wh-ever determiner (whichever, whatever)
EX existential ‘there’
ICS preposition-conjunction (after, before, since, until)
IF ‘for’ as a preposition
II preposition
IO ‘of’ as a preposition
IW ‘with’; ‘without’ as preposition
JA predicative adjective (tantamount, afraid, asleep)
JB attributive adjective (main, chief, utter)
JBR attributive comparative adjective (upper, outer)
JBT attributive superlative adjective (utmost, uttermost)
JJ general adjective
JJ general comparative adjective (older, better, bigger)
JJT general superlative adjective (oldest, best, biggest)
JK adjective catenative (‘able’ in ‘be able to’; ‘willing’ in ‘be willing to’)
LE leading co-ordinator (‘both’ in ‘both…and…’; ‘either’ in ‘either… or…’)
MC cardinal number neutral for number (two, three…)
MC$ genitive cardinal number, neutral for number (10’s)
MC-MC hyphenated number 40-50, 1770-1827)
MC1 singular cardinal number (one)
MC2 plural cardinal number (tens, twenties)
MD ordinal number (first, 2nd, next, last)
MF fraction, neutral for number (quarters, two-thirds)
NC2 plural cited word (‘ifs’ in ‘two ifs and a but’)
ND1 singular noun of direction (north, southeast)
NN common noun, neutral for number (sheep, cod)
NN1 singular common noun (book, girl)
NN1$ genitive singular common noun (domini)
NN2 plural common noun (books, girls)
NNJ organization noun, neutral for number (department, council, committee)
NNJ1 singular organization noun (Assembly, commonwealth)
NNJ2 plural organization noun (governments, committees)
NNL locative noun, neutral for number (Is.)
NNL1 singular locative noun (street, Bay)
NNL2 plural locative noun (islands, roads)
NNO numeral noun, neutral for number (dozen, thousand)
NNO1 singular numeral noun (no known examples)
NNO2 plural numeral noun (hundreds, thousands)
NNS noun of style, neutral for number (no known examples)
NNS1 singular noun of style (president, rabbi)
NNS2 plural noun of style (presidents, viscounts)
NNSA1 following noun of style or title, abbreviatory (M.A.)
NNSA2 following plural noun of style or title, abbreviatory
NNSB preceding noun of style or title, abbr. (Rt. Hon.)
NNSB1 preceding sing. noun of style or title, abbr. (Prof.)
NNSB2 preceding plur. noun of style or title, abbr. (Messrs.)
NNT temporal noun, neutral for number (no known examples)
NNT1 singular temporal noun (day, week, year)
NNT2 plural temporal noun (days, weeks, years)
NNU unit of measurement, neutral for number (in., cc.)
NNU1 singular unit of measurement (inch, centimetre)
NNU2 plural unit of measurement (inches, centimetres)
NP proper noun, neutral for number (Indies, Andes)
NP1 singular proper noun (London, Jane, Frederick)
NP2 plural proper noun (Browns, Reagans, Koreas)
NPD1 singular weekday noun (Sunday)
NPD2 plural weekday noun (Sundays)
NPM1 singular month noun (October)
NPM2 plural month noun (Octobers)
PN indefinite pronoun, neutral for number (none””)”
PN1 singular indefinite pronoun (one, everything, nobody)
PNQO whom
PNQS who
PNQV$ whosever
PNQVO whomever, whomsoever
PNQVS whoever, whosoever
PNX1 reflexive indefinite pronoun (oneself)
PP$ nominal possessive personal pronoun (mine, yours)
PPH1 it
PPHO1 him, her
PPHO2 them
PPHS1 he, she
PPHS2 they
PPIO1 me
PPIO2 us
PPIS1 I
PPIS2 we
PPX1 singular reflexive personal pronoun (yourself, itself)
PPX2 plural reflexive personal pronoun (yourselves, ourselves)
PPY you
RA adverb, after nominal head (else, galore)
REX adverb introducing appositional constructions (namely, viz, eg.)
RG degree adverb (very, so, too)
RGA post-nominal/adverbial/adjectival degree adverb (indeed, enough)
RGQ wh- degree adverb (how)
RGQV wh-ever degree adverb (however)
RGR comparative degree adverb (more, less)
RGT superlative degree adverb (most, least)
RL locative adverb (alongside, forward)
RP prep. adverb; particle (in, up, about)
RPK prep. adv., catenative (‘about’ in ‘be about to’)
RR general adverb
RRQ wh- general adverb (where, when, why, how)
RRQV wh-ever general adverb (wherever, whenever)
RRR comparative general adverb (better, longer)
RRT superlative general adverb (best, longest)
RT nominal adverb of time (now, tommorow)
TO infinitive marker (to)
UH interjection (oh, yes, um)
VB0 be
VBDR were
VBDZ was
VBG being
VBM am
VBN been
VBR are
VBZ is
VD0 do
VDD did
VDG doing
VDN done
VDZ does
VH0 have
VHD had (past tense)
VHG having
VHN had (past participle)
VHZ has
VM modal auxiliary (can, will, would etc.)
VMK modal catenative (ought, used)
VV0 base form of lexical verb (give, work etc.)
VVD past tense form of lexical verb (gave, worked etc.)
VVG -ing form of lexical verb (giving, working etc.)
VVN past participle form of lexical verb (given, worked etc.)
VVZ -s form of lexical verb (gives, works etc.)
VVGK -ing form in a catenative verb (‘going’ in ‘be going to’)
VVNK past part. in a catenative verb (‘bound’ in ‘be bound to’)
XX not, n’t
ZZ1 singular letter of the alphabet:’A’, ‘a’, ‘B’, etc.
ZZ2 plural letter of the alphabet: ‘As’, b’s, etc.

Source: http://ucrel.lancs.ac.uk/claws2tags.html