It means that sth. is considered to be of an acceptable standard or quality; or sth. is morally correct or acceptable; or sb. is honest and behaves in a way that most people approve of.
It refers to is a movement from a higher to a lower level or position; or a surface that slopes downwards, for example the side of a steep hill; or it can be used to talk about a person's family background, for example his/her nationality or social status.