Final answer:
When hemoglobin does not have oxygen bound to it, it is termed deoxyhemoglobin.
Step-by-step explanation:
When hemoglobin does not have oxygen bound to it, it is termed deoxyhemoglobin. Hemoglobin is a protein found in red blood cells that binds to oxygen in the lungs and transports it to the body tissues. When oxygen is released from hemoglobin, it becomes deoxyhemoglobin, which is a darker shade of red.