it's the idea that there is more than one way to be smart. you might be intellectually smart but socially incompetent, or it might be the other way around. Another form is being very visually oriented, or you could be very physically smart and be really intune with your body. perhaps you are great at thinking "sideways" or creatively.
IQ tests are based on just one type of intelligence and essentially test how good you are at being middle class educated and white. there are many other forms of intelligence. Google it for more details.