A brainiac is someone who exhibits a high level of intelligence. This slang term is also used to refer to someone who is particularly interested in science, mathematics, and other intellectual pursuits at a young age, regardless of intelligence level. These people tend to end up in demanding careers that allow them to use their skills and education, and many companies actively recruit them in the interest of developing better products and services.
The origins of this word as a slang term for a very smart person can be traced to a DC Comics villain of the same name who first appeared in 1958. His name is clearly a portmanteau of “brain” and “maniac,” and he used his impressive intellectual abilities for evil, outsmarting heroes like Superman with crafty and elaborate schemes. As a curious side note, many supervillains seem to be extremely intelligent, and intelligent villains are often depicted as elitists who grow frustrated with people of more ordinary intelligence, although real-life brainiacs are, of course, not necessarily villainous or elitist.
This term is usually used with affection, as in “she's such a brainiac,” and it doesn't have the negative connotations sometimes linked with words like “geek” or “nerd,” which are also sometimes used to describe very intelligent people. People may also hear a very smart person referred to as a whiz kid, genius, or Einstein, referencing her or his considerable intelligence.
Brainiacs come in a wide range of varieties. Some are extremely good at mathematics and analytical pursuits, for example, with excellent problem-solving skills and innovative ways of looking at situations. Others may be extremely skilled in the sciences, or they may have an encyclopedic memory about historical events. This term is usually not used to refer to people with unusual talents, such as preternatural skill at the violin, even though such talents often require considerable mental abilities.
Intelligence is a contentious issue among people who study human development. Some people believe that people are born with high intelligence, rather than made, and that only certain people have the potential to become extremely intelligent individuals. Others believe that, given the right environment, anyone can achieve significant intellectual advances, regardless of genetics. The nature vs nurture debate is unlikely to end any time soon, although a number of brainiacs have put their minds to the problem.