Nerd is a derogatory slang term for an intelligent but socially awkward and obsessive person who spends time on unpopular or obscure pursuits, to the exclusion of more mainstream activities. Nerds are considered to be awkward, shy, and unattractive. Thus, a nerd is often excluded from physical activity and considered a loner

Loner

A loner is a person who avoids or does not actively seek human interaction or prefers to be alone. There are many reasons for solitude, intentional or otherwise, and "loner" implies no specific cause. Intentional reasons include spiritual and religious considerations or personal philosophies...

 by others, or will tend to associate with a small group of like-minded people.