Final answer:
A 3-D surface designed to be viewed from only one direction is known as a relief, which is distinct from a freestanding sculpture in the round meant to be viewed from multiple angles.
Step-by-step explanation:
A 3-D surface that is designed to be viewed from only one direction is known as a relief. Unlike sculpture in the round, which is freestanding and designed to be observed from all sides, a relief sculpture is one that projects from a background and does not fully detach from it. The term mass in the context of art refers to the three-dimensional volume of a piece of artwork, which gives it perceived weight and density. A relief might come in the form of high-relief, where the sculpture projects significantly from the background, or low-relief (also known as bas-relief), where the protrusion is shallow. It's important to differentiate this from form in the round, which is meant to be viewed from any angle and is freestanding.