Because most loudspeakers are placed in front of musicians to reduce
the possibility of feedback, many mixers have the ability to send a
second “mix” to loudspeakers called monitors that usually face
musicians or those speaking or performing so that they can hear
themselves. This mix is called a “monitor mix.”
This “monitor mix” also needs power and may require a second amp, unless you have a powered mixer or portable PA that may have a built-in amp for your monitor mix.