Blood donation is the process of giving blood to be used for medical purposes, including blood transfusions. Some blood donors are able to give blood platelets by apheresis; the process is lengthier (around two hours per donation) but can be undertaken every four weeks, rather than around three times a year for regular donation.
Some religious groups such as Jehovah's Witnesses do not agree with the donation or receipt of blood for conscientious reasons.
People with a high risk of spreading HIV are not allowed to give blood. For prostitutes, etc., they avoid risky behavior for one year.