A percussion instrument is any object which produces a sound by being hit with an implement, shaken, rubbed, scraped, or by any other action which sets the object into vibration. The term usually applies to an object used in a rhythmic context or with musical intent.
In a musical context then, the term "percussion instruments" may have been coined originally to describe family of instruments including drums, rattles, metal plates, or wooden blocks which musicians would beat or strike (as in a collision) to produce sound.