Most people that have heard of introversion and extroversion associate both words with very specific traits. If you were to ask how the average person would describe an extrovert, the answers would typically vary from "outgoing" to "talkative" while an introverted person would most likely be described as "quiet" or "shy."
As someone who is more introverted, I've definitely related to that feeling of wanting to stay in with a book most nights. There's that nagging, almost guilty feeling of relief when plans are canceled and I'm able to stay home.
But I've also had plenty of other days where I felt more like going out and having fun with my friends. Likewise, even the most extroverted person will have times when they'd rather relax on the couch and watching some Netflix instead of going out to a party.
In reality, most people are balanced, or a mixture of both, on the psychological spectrum of introversion/extroversion, although they may lean towards one side or the other. Carl Jung, the man who first coined the terms introverted and extroverted, is claimed to have said,
"There is no such thing as a pure introvert or extrovert. Such a person would be in the lunatic asylum."
This is most likely true since the majority of the population would find it a nightmare scenario to never have any human company ever, or to only ever have human company without ever having a moment of time to themselves.
But what's the difference between these two traits? Is it really as simple as how talkative or outgoing (or not) you are? And is one naturally better than the other?
There are a lot of ways to describe it, but what separates introversion and extroversion boil down to this: while introverts typically "recharge" by spending time alone or in less stimulating environments, extroverts are more energized by spending time in environments where there might be more people, noise, etc.
Scientifically, this is because of differences in the nervous system between introverts and extroverts. While extroverts normally have stronger "dopamine" reactions in more stimulating environments, introverts seem to prefer a different type of neurotransmitter called acetylcholine, which is linked with a part of the brain that deals more with turning inwards or removing yourself from the environment. The biological basis for these personality traits is pretty interesting when you get down to it.
However, this doesn't mean that introverts are shy, antisocial, and don't like people, or that extroverts are all loud party animals.
In fact, despite the words "introvert" and "shy" often being used interchangeably, they really aren't related at all. A person could be extroverted and shy. For example, someone who absolutely loves being around people, but still hates being the center of attention. Conversely, an introverted person could be extremely confident and bold (when they can be persuaded to leave the house).
In American culture, extroverted traits are typically seen as more ideal and are usually associated with success and leadership.
Truthfully, though, neither trait is "better" than the other.
While some people are more productive working with others or in an environment where there are lots of people around, other people are more productive working solo, and that's just the way it is.