The short answer: An introvert is someone who gains energy by being alone, while an extrovert recharges by being social. Still others, called ambiverts, are in the middle.
The long answer: There are actually many definitions of the words introvert and extrovert. In terms of Jungian psychology, an introvert is a person who is primarily turned inward, towards their thoughts and feelings, while extraverts are directed outwards, to things outside the self.
You may have also come across a definition referencing stimulation. Hans Eysenck theorized that we all have a base level of cortical arousal. Introverts have a higher baseline level of arousal and therefore need less stimulation (like staying at home and reading). Extroverts, on the other hand, have a lower baseline level of arousal, and so they tend to seek out sources of stimulation (like parties). Ambiverts are in the middle.
But whatever definition you use, please do not use the word shy to describe introversion.
Characteristics that many introverts can relate to:
• Dislikes small talk
• Likes nature
• Enjoys working independently vs group projects
• Gets really excited and talkative when speaking about something they love
• Trouble formulating on-the-spot answers to questions
• Sensory overload, as in getting uncomfortable/overwhelmed after too many sights, sounds, etc, (if this describes you, you may be a Highly Sensitive Person)
• “Shutting down” or getting grumpy after prolonged social interaction
• Dislikes open-plan offices
• Focuses on work vs chit-chatting with coworkers
• Has a few close friends
• Dislikes parties
• Prefers texting or emailing rather than speaking on the phone
If only a few of those describe you, and you consider yourself to be an introvert, that’s fine by me.