A percussion or concussion instrument is a musical instrument that is sounded by being struck or scraped or struck by a beater. This includes attached or enclosed beaters or rattles that are struck by hand or by another similar instrument. The percussion family is believed to include the oldest musical instruments, following the human voice.
The percussion section of an orchestra most commonly contains instruments such as timpani, snare drum, bass drum, cymbals, triangle and tambourine. However, the section can also contain non-percussive instruments, such as whistles and sirens, or a blown conch shell. Percussive techniques can also be applied to the human body, as in body percussion.
On the other hand, keyboard instruments, such as the celesta, are not normally part of the percussion section, but keyboard percussion instruments such as the glockenspiel and xylophone [which do not have piano keyboards] are included.
Percussion instruments are most commonly divided into two classes: Pitched percussion instruments, which produce notes with an identifiable pitch to which xylophones [balafon, marimba] fall under and unpitched percussion instruments like the udu, wood block and clave, which produce notes or sounds without an identifiable pitch.
111.1 There are two main categories of directly struck idiophones, concussion idiophones and 111.2 percussion idiophones.
111.1 Concussion idiophones or clappers.
111.2 Percussion idiophones.
The instrument is struck either with a non-sonorous object hand, stick, striker or against a non-sonorous object – human body, the ground.
111.11 Concussion sticks or stick clappers, nearly equal thickness and width.
111.12 Concussion plaques or plaque clappers, flat.
111.13 Concussion troughs or trough clappers [shallow].
111.14 Concussion vessels or vessel clappers [deep].
111.141 Castanets – Natural and hollowed-out vessel clappers.
111.142 Cymbals – Vessel clappers with manufactured rim.
111.2 Percussion idiophones
The instrument is struck either with a non-sonorous object such as a hand, stick, striker or against a non-sonorous object or human body, the ground.
111.21 Percussion sticks.
111.211 Individual percussion sticks – Dhantal, Triangle,
111.212 Sets of percussion sticks in a range of different pitches combined into one instrument. All xylophones, as long as their sounding components are not in two different planes.
Gandingan a kayo
Kulintang a kayo
Luntang or kwintangan kayo
Marimbaphone [also bowed]
111.22 Percussion plaques.
111.221 Individual percussion plaques.
111.222 Sets of percussion plaques – Examples are the Lithophone and also most Metallophones.
Kulintang a tiniok, kulintang a putao, or sarunay
Ranat ek lek
Ranat thum lek
111.23 Percussion tubes.
111.231 Individual percussion tubes.
Agung a tamlang
Krin or Kolokolos
Tubular Wood block
111.232 Sets of percussion tubes.
Tubular bells or chimes
111.24 Percussion vessels.
Kagul or tagutok
Steel-pan or steel drum
Udu [also an aerophone]
111.241 Gongs – The vibration is strongest near the vertex.
111.241.1 Individual Gongs.
111.241.2 Sets of Gongs.
Agung or agong
Kulintang or kolintang
111.242 Bells – The vibration is weakest near the vertex.
111.242.1 Individual bells
111.242.11 Resting bells whose opening faces upward – Cowbell
111.242.12 Hanging bells suspended from the apex.
111.242.121 Hanging bells without internal strikers.
111.242.122 Hanging bells with internal strikers.
111.242.2 Sets of bells or chimes.
111.242.11 Sets of resting bells whose opening faces upward.
111.242.12 Sets of hanging bells suspended from the apex.
111.242.121 Sets of hanging bells without internal strikers.
111.242.122 Sets of hanging bells with internal strikers.
Indirectly struck 112 Indirectly stuck idiophones produce sound resulting from an indirect action of the performer as opposed to the directly struck idiophones.  The player himself does not go through the movement of striking; percussion results indirectly through some other movement by the player. This category is divided in two main sub-categories: shaken idiophones and scraped idiophones.
Shaken idiophones or rattles [112.1] Further information: Rattle percussion instrument – The player makes a shaking motion
112.11 Suspension rattles – Perforated idiophones are mounted together, and shaken to strike against each other.
112.111 Strung rattles – Rattling objects are strung in rows on a cord.
112.112 Stick rattles – Rattling objects are strung on a bar or ring.
112.12 Frame rattles – Rattling objects are attached to a carrier against which they strike.
112.121 Pendant rattles.
112.122 Sliding rattles.
112.13 Vessel rattles – Rattling objects enclosed in a vessel strike against each other or against the walls of the vessel, or usually against both.