Ultrasound is a medical imaging technique that uses high frequency sound waves to create images of internal body structures. It is non-invasive, safe, and painless, and can be used to visualize organs, blood vessels, and tissues in real-time. Ultrasound is commonly used during pregnancy to monitor fetal development, but it is also used to diagnose a variety of medical conditions, such as tumors, gallstones, and heart disease. Additionally, ultrasound can be used to guide certain medical procedures, such as biopsies and injections.