Orbit is the trajectory of an object moving in a circular, elliptical, or hyperbolic path around a bigger object, attracted by its gravity. Mars and other planets are orbiting the Sun in an elliptical trajectory. Mars is orbited by two moons: Phobos and Deimos.
Low Earth Orbit is the minimum hight (160 km) and velocity (8 km/s) that an object needs to stay in orbit round Earth. This orbit is the easiest to reach with currently available rocketry. It might be used to assemble a large spaceship from smaller parts that are lifted separately from Earth.