Which of the following describes a condition where a joint is unable to move?

The term that describes a condition in which a joint is unable to move is ankylosis. This condition occurs when the joint becomes stiff or rigid due to the abnormal fusion of bones, which can result from various factors such as inflammation or injury. In ankylosis, the normal movement of the joint is significantly restricted or completely lost, leading to a loss of function in that particular area.

Understanding this term is vital in the medical field, as it helps in diagnosing joint-related conditions and planning appropriate treatments. The other terms listed refer to different medical conditions: angina relates to chest pain due to reduced blood flow to the heart, anemia involves a deficiency of red blood cells or hemoglobin, and aphasia is a communication disorder affecting a person's ability to use language. Recognizing these definitions serves to clarify the specific nature of ankylosis in contrast to other health issues.