A donor in general is a person who donate

Donation

A donation is a gift given by physical or legal persons, typically for charitable purposes and/or to benefit a cause. A donation may take various forms, including cash, services, new or used goods including clothing, toys, food, and vehicles...

s something voluntarily. Usually used to represent a form of pure altruism

Altruism

Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...

 but sometimes used when the payment for a service is recognised by all parties as representing less than the value of the donation and that the motivation is altruistic. In business law, a donor is someone who is giving the gift, and a donee the person receiving the gift.

Often the word is used as a shorter term for:

• Blood donor
  Blood donation
  A blood donation occurs when a person voluntarily has blood drawn and used for transfusions or made into medications by a process called fractionation....
  
  
• Electron donor
  Electron donor
  An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process....
  
   — (by analogy) a technical term in chemistry and semiconductor
  Semiconductor
  A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
  
   physics (see also the next entry)
• Donor (semiconductors)
  Donor (semiconductors)
  In semiconductor physics, a donor is a dopant atom that, when added to a semiconductor, can form n-type regions.For example, when silicon , having four valence electrons, needs to be doped as an n-type semiconductor, elements from group V like phosphorus or arsenic can be used because they have...
  
  
• Organ donor
  Organ donation
  Organ donation is the donation of biological tissue or an organ of the human body, from a living or dead person to a living recipient in need of a transplantation. Transplantable organs and tissues are removed in a surgical procedure following a determination, based on the donor's medical and...
  
  
• Sperm donor
  Sperm donation
  Sperm donation is the provision by a man, , of his sperm, with the intention that it be used to impregnate a woman who is not usually the man's sexual partner, in order to produce a child....
  
  
• Charitable donor
  Charitable organization
  A charitable organization is a type of non-profit organization . It differs from other types of NPOs in that it centers on philanthropic goals A charitable organization is a type of non-profit organization (NPO). It differs from other types of NPOs in that it centers on philanthropic goals A...
  
  
• Egg donor

In art:

• donor portrait
  Donor portrait
  A donor portrait or votive portrait is a portrait in a larger painting or other work showing the person who commissioned and paid for the image, or a member of his, or her, family...
  
  , portrait of the person who paid for a painting, typically in a church

In literature:

• Donor (fairy tale)
  Donor (fairy tale)
  In fairy tales, a donor is a character that tests the hero and provides magical assistances to the hero when he succeeds.The fairy godmother is a well-known form of this character...
  
  is a stock character of fairy tales