A synthetic diamond is a man-made diamond that has been created in a laboratory using a process called high pressure, high temperature (HPHT) synthesis. This involves subjecting carbon-based materials to extreme conditions similar to those found deep within the Earth's crust where natural diamonds are formed. The result is a diamond with identical chemical and physical properties to a naturally occurring diamond, including its hardness and brilliance. Synthetic diamonds can be used for various purposes such as jewelry, industrial applications, and scientific research.