A drum kit is a collection of drums, cymbals and other percussion instruments arranged for convenient playing by a sole percussionist (drummer), usually for jazz, rock, or other types of contemporary music. Such a kit has been an integral part of most popular music since the jazz of the 1920s until the arrival of synthesised percussion replaced drums in some electronic music.
Early drum kits were known as traps kits and consisted of a pedal-operated bass drum, a snare drum on a stand, a small cymbal and other small percussion instruments mounted on the bass drum or a small table, all played with drum sticks or brushes except for the bass drum. This name now survives in the term traps case still given to a case used by a kit drummer (or any percussionist) to transport stands, pedals, sticks, and miscellaneous percussion instruments other than drums and cymbals.
An extended 4-piece kit
The exact collection of percussion instruments in a drum kit varies greatly according to the style of music being played and the preferences (and financial resources) of the drummer, but at a minimum a kit usually contains a bass drum mounted on the floor and played with a pedal, a snare drum on a stand, two or three tom-tom drums, some of which are mounted on top of the bass drum and the largest typically free-standing alongside it (on the floor - hence the word "floor tom"), a hi-hat (usually to the left of the bass drum, near the snare), a ride cymbal and a crash cymbal arranged on stands so that they are conveniently reachable above the snare and tom-toms. The drummer sits directly behind the bass drum, with their left foot on the hi-hat's pedal and their right on the bass pedal. They will be equipped with either drumsticks or brushes to play the other instruments in the kit.
Additions that drummers add may include a second bass drum, additional toms (either extending the range of the original set or occasionally providing a second set with a different tone), more cymbals, tambourines, woodblocks, cowbells, and electronic pads that trigger synthesisers when struck by a drumstick, amongst others. Some drummers, such as Neil Peart and Terry Bozzio have gone to extreme lengths and built massive kits including features such as ranges of tuned tom-toms, allowing them to contribute melodically as well as rhythmically.