rhythm instrument       
noun [ C ] uk/ˈrɪð.əm ˌɪn.strə.mənt/ us/ˈrɪð.əm ˌɪn.strə.mənt/
 节奏乐器
a musical instrument that is played to provide a strong beat to a piece of music
  He uses his guitar as a supporting rhythm instrument. 他用吉他作为辅助节奏乐器。 
 Members of the choir danced in the aisles with tambourines and other rhythm instruments. 合唱团成员演奏着手鼓和其他节奏乐器在教堂侧廊翩翩起舞。 
 - More examples
 - He often played bass guitar as a lead rather than rhythm instrument giving The Who their unique sound.
 - The Roland TR-808 drum machine was the rhythm instrument of choice on many early '80s dance records.
 - Madness was mostly content to keep its horns as rhythm instruments.