Altruism is the principle or practice of unselfish concern for or devotion to the welfare of others. It involves acting for the benefit of someone else, even at a cost to oneself. This can range from small acts of kindness, like helping a stranger with directions, to significant sacrifices, such as donating a kidney. Altruistic behaviors are motivated by a desire to improve another's well-being, not by any expectation of personal gain. For example, volunteering at a homeless shelter is an act of altruism, as the volunteer's primary motivation is to help those in need.