Is there a word to describe the virtue of "to do something and ask for nothing in return"?

I am wondering if there is a positive, formal counterpart to the slang "No strings attached" to describe, for example, a parent's unquestioned devotion to their children, or the virtue of someone's "a friend in need is a friend in deed", help first, question later mentality.

Answer

I think the word you are looking for is altruism

altruism, n.

Pronunciation: Brit. /ˈaltrʊɪz(ə)m/ , U.S. /ˈæltrəˌwɪzəm/ , /ˈælˌtruˌɪzəm/

1. Disinterested or selfless concern for the well-being of others, esp. as a principle of action. Opposed to selfishness, egoism, or (in early use) egotism.

OED