Based on this paragraph, give me a summary of what a kidney donor chain is.
When a donor wishes to give their kidney to a specific patient but they are not a match with that patient, they can join a kidney donor chain to accelerate the process of finding an organ for the patient. In exchange for giving their kidney to another patient, the patient they had wanted to help can be paired with another donor who is a match for them but not for the patient to whom they wish to donate their kidney.