When a galvanic cell is comprised of an anode and a cathode of precisely the same material, this is called a(n):

Concentration cell

Explanation:

Galvanic cells and even electrolytic cells usually consist of two electrodes namely anode and cathode. These 2 electrodes can either be made of the same metals or different metals, and also an electrolyte whereby the two electrodes are immersed.

Now, in the case where the electrodes are made of the same metal, we call it a concentration cell because A concentration cell is a cell that consists of two half-cells that have the same electrodes, but yet differ in concentrations.

where's the diagram?

let that person have a turn to speak : )