Which term describes a malignant tumor?

The term that describes a malignant tumor is "sarcoma." This is because "sarcoma" specifically refers to cancers that arise from connective tissues such as bone, cartilage, fat, muscle, or vascular tissues, making it the correct designation for malignant tumors originating in these types of structures.

In contrast, "oma" generally refers to benign tumors. Although some "oma" terms can represent malignant conditions (like melanoma), they are not exclusively used for cancer, which is why they do not fit this particular question as well as "sarcoma." The term "plasm" refers to a formation or growth but does not specifically indicate malignancy, whereas "-stasis" relates to the stopping or controlling of flow but is not associated with tumor classification at all. Thus, "sarcoma" stands out as the appropriate choice for malignancy in context to tumors.