Ultrasound is a medical imaging technique that uses high-frequency sound waves to create images of internal organs and structures in the body. It is a non-invasive and painless procedure that is commonly used for diagnostic purposes, such as determining the health of a fetus during pregnancy or identifying abnormalities in various organs. Ultrasound can also be used for therapeutic purposes, such as breaking up kidney stones or promoting healing in soft tissues. Overall, ultrasound is a versatile and safe imaging modality that is widely used in medical practice.