Despite a long history of research and debate, there is still no standard definition of intelligence.The article is more optimistic than that quote makes it out to be. The authors list 71 definitions of intelligence used in different fields of study but seem to be optimistic about finding some unifier for all of them that will give a general definition for the word.
There have been times when I have been particularly frustrated talking with people about intelligence because most people have a vague definition that is more about making people feel good than attempting an objective way to discuss it. We don't want to find out that we or the people we care about or the people we agree with are unintelligent so we have all agreed to accept the "everybody is intelligent in their own way" line. It might be useful to reframe the conversation to acting intelligent instead of being intelligent (or having intelligence) for the sake of losing the personal label and making people more open to accepting objective standards.
Granted there is probably a lot of truth to being intelligent. Some people have more capable brains than others and that's just the way it is. The only reason we would adopt this concept of intelligence would be to make an objective definition of it more palatable for society. We may have to postpone using objective-adjective intelligence for objective-adverb intelligence until we're mature enough to accept that the people we like and agree with may not be as smart as the people we don't like and disagree with.