[wikitionary definition: (music) A style/sub-genre of hip hop characterized by hard-hitting drums, usually containing the kick-drum/snare drum/hi-hat combination rather than claps, snaps, TR-808 bass drums, cowbells, shakers, and various other percussion sounds used for rhythm.
A beat made with the 808 drum kit isn't boom bap!]

Descripitive of the drum patterns in (as well as the feel of) real, raw Hip-Hop tracks, particulary, of the 1988-1998 era. Taken from the phonetic sound of old school hip-hop drum sampled patterns - 'boom = kick' (i.e. hard hitting bass drum) 'bap' = 'snare' or 'high hat' (i.e. sharp snapping snare drum or high hat cymbal) that is often EQed to the forefront of the beat, which often lends it a darker atmospheric underground feel. Mostly these drum sounds are sampled from 70s Funk breaks.

typical pattern: "1, 2, 3 and , 4 and" = "boom, bap, boom boom, bap boom" - (with the "and" being on the half beat)
typical pattern: "1, 2, 3 and , 4 and" = "boom, bap, pause boom, bap boom" - (with the "and" being on the half beat)

Also worth noting is that many foundation Bboy and Hip Hop dance moves have been deliberatly structured to or naturally fit these beat patterns. A true Bboy will dance on-beat aiming to hit their gestures/shapes or freezes on the "bap" (snare/high hat) which accentuates and shows awarness of the beat and it's rhythm to the viewer but can also make the visual effect of the move much greater also.

click here to listen to an early example of these patterns in use ('The Bridge' instrumental produced by Marley Marl in 1986)

"With a kick, snare, kicks and high hat. Skilled in the trade of that old boom bap"
is originally from A Tribe Called Quest song "We Can Get Down"
Other notable Boom Bap artists include: Tha Alkaholiks, The Beatnuts, Beastie Boys, Big Daddy Kane, Brand Nubian, Cypress Hill, Das EFX, Diamond D & The Psychotic Neurotics, EPMD, Gang Starr, House Of Pain, Ice-Cube, Jungle Brothers, Krs One (his 1993 album was also named "Return Of The Boombap"), King Tee, Leaders Of The New School, Lord Finesse, Lords Of The Underground, Main Source, Masta Ace, Mobb Deep, N.W.A., The Pharcyde, Tim Dog, Wu-Tang Clan

BUBBLE LETTERS
A widely used soft rounded Bronx lettering style (also known as SOFTIE LETTERS)

BUFF
To erase. Any means employed by the Transit Authority to remove graffiti from trains

BURN
To best, defeat or upstage, usually in competition (also known as ROAST)

BURNER
A well-done Hip-Hop creation (e.g. Graffiti Artwork, Bboy set, DJ set, MC freestyle etc) that beats the competition. A burner is a winner

C
CAP (Fat, Skinny etc)
Interchangeable spray-can nozzles fitted to can to vary widths and types of spray

CATS
People, usually male

CHILLIN'
Being out there and being cool. Relaxing.

CLIQUE
Loosely organised group of writers, dancers, MCs, DJs. Also known as a CREW

CLOUD
A design for the background of a graffiti piece. Usually created spontaneously when painting to cover over anything else already on the surface and avoid it visually interfering with the design

CREW
Loosely organised group of writers, dancers, MCs, DJs. Also known as a CLIQUE

D
DEF
Really good (derived from 'death' apparently)

DING DONG
Relatively new stainless-steel type of subway car, so named for the bell that rings just before the doors close

DISSED / DISS
Disrespected / to disrespect

D.L.
To keep secret / to have or assume ill knowledge of. As in Down Low, a play on Lowdown

DOPE
Good or better than good

DOWN
In, part of the group or action (e.g. "He's down with us")

DUBS (also known as THROW-UP)
A name painted quickly with one layer/colour of spray paint and an outline. Often done using BLOCKBLUSTER or BUBBLE letters for speed and simplicity

E
END TO END
A piece or painting the length of a subway car (WINDOW DOWN or TOP TO BOTTOM)

F
FADE
To blend colours when spray-painting

FEET / FOOT LETTERS (also known as HUMP LETTERS)
A letter with a rounded protrusion bottoms/backs

FILL-IN
Colouring of a piece or other forming

FLAT
Older slab-sided type of subway car; the most suitable surface for painting

FLY
Top notch, good or looking good, above average

FORCE-FIELD
A secondary outline (usually contrasting in colour to allow the letter/piece to stand-out from the background and clearly define shape of piece) painted around the main outline on Graffiti Art letters/pieces

FRESH (see also STUPID FRESH)
Very good - innovative and original

FRONT
Pretend, lie, more talk than action, falsely represent

FUNKY
Good or better than good. Above ordinary

G
GETTING AROUND
Having ones name in quantity or in many places

GETTING UP
successfully hitting a train or wall (i.e. you effectively got your name UP)

GETTING MINE
to get what one desrves or deserves

GOING FOR BROKE
Taking an action to the extreme

GOING OFF
Taking an action to the extreme

GOING OVER
One writer covering another writer's name with his own

GRAFFITI
The plural of grafitto. Also the term created by the media to refer to 'writing' when first reporting on the culture in the 1970s

GRAFFITO
Drawing or writing using ink or a medium on a wall or surface

H
HARDCORE
Totally beyond or above the norm

HEART BOTTOM LETTERS
Letters with heart shaped bottoms

HIT
To TAG up any surface with paint or ink

HOT 110
A name used to write over those who write over others

HUMP LETTERS (also known as FEET / FOOT LETTERS)
A letter with a rounded protrusion bottoms/backs

K
KING
The best with most. Usually declared by many about another. (e.g. "He's the KING of style"). In graffiti, those declared as KINGS will often add a crown above their TAG or PIECE

L
LAY-UP
An underground or elevated siding where trains are parked when not in use

LOAF
A half circle/oval that comes of a letters end

M
MACHINE LETTER
A machine like lettering style

MARRIED COUPLE (MAC)
Two subway cars permanently attached, indentified by their consecutive numbers

MARSHMALLOW
A lettering style with puffy bottoms

MASTERPIECE
A combination of outlined and filled in stylised letters

MECHANICAL LETTER
A mechanical like lettering style

N
NA MEAN?
Know what I mean? / Understand?

NAME BELT
A customisable metal belt buckle, from early Hip Hop fashion, featuring your own bboy/writer etc 'name', usually in silver or gold

O
OLD SCHOOL / SKOOL
Original, a specific era, day one

OUTLINE
A pieces structure / hollowed out shell

P
PANEL PIECE
A painting below the windows and between the doors of a subway car

PENMANSHIP
n. The art, skill, style, or manner of handwriting; calligraphy

PHYSICALS
Friends or individuals

PIECE
A painting, short for masterpiece
TO PIECE
To paint graffiti art

PIECE BOOK (also known as a BLACK BOOK)
A writer's sketchbook

PLATFORM LETTER
A stemmed or extended letter style or accessory

PROPS or PROPERS
Respect or dues

R
RIDGY
Subway car with corrugated, stainless-steel sides, unsuitable for graffiti

ROAST (also known as BURN)
To best, defeat or upstage, usually in competition

S
SANDWICH
A cut [letter] segment of three or more layers

SINGLET
The original name for a TAG

SOFTIE LETTERS (also known as BUBBLE LETTERS)
A widely used soft rounded Bronx lettering style

STAR LETTERS
Letters with star shaped protrusions

STUPID FRESH (see also FRESH)
Superlatively good

STYLE-WRITER (also see WRITER)
practioner of the Art of graffiti, particularly as an occupation
(the 'Style-Writer' term was coined after the original term 'Writer' by Phase 2 to differenciate from those who are authors, typists etc)

T
TAG
A writer's signature with marker or spray paint

TAGGING UP
The act of writing your name with marker or spray paint

THROW-UP (also known as DUBS)
A name painted quickly or scarcely with one layer/colour of spray paint and an outline. Often done using BLOCKBLUSTER or BUBBLE letters for speed and simplicity. Most notably popularised by 'IN/KILL3'

TOP-TO-BOTTOM
A piece which extends from the top of the subway car to the bottom

TOY
Inexperienced or incompetent writer, originally one with no status or recognition usually due to lack of experience or masterpieces

U
UP
Describes a writer whose work appears regularly on the trains and walls

V
VANDAL
Wilful or ignorant destroyer or damager of works of art or property, for the sake of destruction

W
WAK or WACK
Substandard or incorrect (derived from "out of whack")

WHOLE CAR
A piece or painting expanding a subway cars width and length

WILDSTYLE
A complicated construction of interlocking letters

WINDOW-DOWN
A piece or painting done below the windows of the subway car

WINDOW-DOWN END TO END (WIDEE)
A piece or painting done the full length and below the windows of a subway car

WRITER (also see STYLE-WRITER)
Practioner of the Art of graffiti, particularly as an occupation

WRITING
The act of one who writes / uses marker or spray paint (to create their name or artwork)