What makes the Calvin cycle a cycle?

Answer 1

The Calvin cycle is called a cycle because the catalysts are recycled and used again repeatedly and continuously (i.e. a circular process).

Answer 2

The Calvin cycle is a cycle because it begins and ends with the same molecule, ribulose-1,5-bisphosphate (RuBP). This molecule is regenerated at the end of the cycle after it undergoes a series of reactions that produce sugars used by the plant for energy.