A drummer is a musician who plays drums, which includes a drum kit ("drum set" or "trap set", including cymbals) and accessory-based hardware which includes an assortment of pedals and standing support mechanisms, marching percussion or any musical instrument that is struck within the context of a wide assortment of musical genres. The term percussionist applies to a musician who performs struck musical instruments of numerous diverse shapes, sizes and applications. Most contemporary western ensembles bands for rock, pop, jazz, R&B etc. include a drummer for purposes including timekeeping. Most drummers of this particular designation work within the context of a larger contingent (aka rhythm section) that may also include, keyboard (a percussion instrument) or guitar, auxiliary percussion (often of non western origin) and bass (bass viol or electric). Said ensembles may also include melodic based mallet percussion including: vibraphone, marimba or xylophone. The rhythm section, being the core metronomic foundation with which other melodic instruments, including voices, may present the harmonic/melodic portion of the material.