"Dorsal" refers to the back side of the body whereas "ventral" refers to the front side of the body. When discussing bipeds, these terms are interchangeable with the terms "posterior" and "anterior."
These terms can become confusing when talking about both bipeds and quadrupeds. The terms "dorsal/posterior" and "ventral/anterior" are only interchangeable for creatures that walk on two legs and stand upright. With an animal that stands on four legs, such as a dog, the head is referred to as the anterior and the tail as the posterior, while the back is referred to as dorsal and the belly as ventral. In quadrupeds like the dog, "anterior" and "posterior" are synonymous with the words "cranial" and "caudal."
These terms are more difficult to use with invertebrate and asymmetrical creatures. Due to the wide variety of body shapes prevalent in such creatures, terms are usually borrowed from vertebrate anatomy and additional terms, such as "proximal," are used to clarify location. Proximal literally means "near."
The terms "dorsal" and "ventral" are not applicable to every organism in existence. Amoebae change shape constantly, so such terms are useless when describing them. In elongated organisms like sponges, which attach themselves to a surface, the terms can be used as the sponge has identifiable ends.