What is characterized as a small, irregularly shaped body composed of water, ice, rock, and frozen gases?

The choice describing a small, irregularly shaped body composed of water, ice, rock, and frozen gases is a comet. Comets are often referred to as "dirty snowballs" because they contain a mixture of volatile ices and solid particles. When they approach the sun, the heat causes the ice to sublimate, creating a glowing coma and often a tail that can be millions of kilometers long. This unique combination of materials and the behavior of comets as they move through the inner solar system distinguishes them from other celestial bodies such as asteroids, planets, and lunar rocks, which have different compositions and characteristics.

Asteroids, for instance, are primarily made of rock and metal and do not have the icy components typical of comets. Planets are larger and have a more spherical shape. Lunar rocks are specific to the Moon and do not fit the criteria outlined in the question. Thus, comets are the best match for the characteristics described.