A Hohmann Transfer Orbit is an efficient way to move a spacecraft between two circular orbits around a celestial body, such as a planet. It involves two engine burns: the first burn increases the spacecraft's speed to reach an elliptical orbit that touches both the lower and higher orbits, while the second burn occurs at the higher orbit to circularize it. This method minimizes fuel consumption, making it a popular choice for missions within our solar system. The concept was developed by Walter Hohmann, a German engineer, in the early 20th century and remains a fundamental principle in orbital mechanics.