A stethoscope is a medical device that is used to listen to peoples hearts, stomach, lungs and other parts of the body.
The stethoscope is placed on the persons skin and then it amplifies the sounds so that the doctor can hear those sounds much easier than without the stethoscope.
The stethoscope helps the doctor check for heart issues, lung issues and much more and is also used to check a persons blood pressure.
The stethoscope has two different ends which is louder than the other one so the doctor can use the correct end of the stethoscope.
You can buy a stethoscope for at home use as well and learn to listen to your own lungs, heart etc so that you can detect issues and let a doctor know about it.