The difference between Introverts and Extroverts is whether you are drained or recharged from social interactions. I think that's the most insightful definition I've heard.
That's actually not true, though. Even extroverts get drained from social interactions. It just takes longer. And like with everything psychology, it's a spectrum. And not a one-dimensional at that.
Social interactions are mentally tiring. There are generally more things to keep track of and keep in mind at all times than when you're alone. So both introverts and extroverts get tired by social interactions, but they're differently able at handling those situations.
On the other hand, most people require some amount of social interaction to not feel lonely, and at the extreme end, stay mentally sane. Social stimulation can help ground us and maintain a sense of belonging among people. This is more or less the opposite of the previous part. Introverts generally need less social interaction, while extroverts need more.
And of course, those vary from individual to individual. And there are more factors to it. Some people can go from party to party and not feel drained, but also be alone with their thoughts for extended periods of time without any anxiety. Others are the opposite, and can barely handle any social interactions, but still get lonely quickly.
All in all, it's complicated, and no simplification holds true for everything.
