When I think of intelligence I think of the kind of people that are able to both take in and recall all kinds of information as well as understand the deeper concepts within that information such as the relation between things, the cause and effect, and details about how things function. Although there are different kinds of intelligence, that is the kind I think of when someone brings up the term, because I personally assign other types of intelligence different titles.
I definitely appreciate intelligence in other people, but like most people I stay with people around my level of intelligence. Some people can easily get into discussions over my head.
As far as picturing unintelligent people, you know what I think it is for me that makes people stand out, it's the ones that have no intention or desire to learn. They get stuck at a certain level and are content with it. Unfortunately, I'd say that the cause of this is usually parenting styles that don't put importance on expanding one's mind. School can kill the desire to learn as well. But a lot of people are given the opportunity and just don't try.
Adding to what Digital said, I also think we do judge the intelligence of people by their abilities (or inabilities) to communicate. A low vocabulary (and by that I mean using the amount of words a five year old might use in conversation) tends to make someone look less intelligent. There's no need to be highfalutin, but being so limited in the way you choose to express yourself (even though there are so many more options) shows, once again, that you don't put much value on learning. Therefore, you appear less intelligent.
