As Dr. Howard Gardner discovered, there are many different kinds of intelligence. This is a concept that is very important and should be taken into consideration when thinking about how "smart" someone is. Just because they're not so great at spelling does not mean they're also terrible at solving math problems. This is because those are two separate types of intelligence. So how do we decide if someone is an overall intelligent person? The IQ test is not a very reliable source for that because it does not measure all of the intelligences.
This article takes the 9 different kinds of intelligence -- linguistic, logical-mathematical, musical, spatial, bodily-kinesthetic, interpersonal, intrapersonal, naturalistic, and existential--and explains them in an easy-to-understand way. It's important for people to realize that intelligence comes in many different forms and that if someone lacks in a certain area of intelligence, they make up for it in another. People that are very intelligent musically, but not linguistically (reading, writing, etc.) are still very smart and can still do something with their specific intelligence. They could be a genius in the musical area but not get linguistics at all, and that doesn't mean that they are not intelligent. Another thing that needs to be realized is that there are ways to strengthen the intelligence that you lack. For example, if you're lacking in bodily-kinesthetic intelligence, you can do yoga, crafts or dance to increase this ability. There are many ways that humans can branch out and be smart in different areas other than the standard IQ test definition of intelligence and this is seen in Howard Gardener's multiple intelligence theory.