What object is referred to as a dirty snowball?

A "dirty snowball" refers to a comet. This term describes the composition of comets, which consist of ice, dust, and rocky material. When comets approach the sun, the heat causes the ice to vaporize, creating a glowing coma and tail that can be visible from Earth. The "dirty" aspect comes from the inclusion of dust and other non-icy substances mixed with the frozen components.