science

In addition to Aezora's response, extrovert vs introvert being a description of your attitude to socializing is only a colloquial use of the term. I am a shy extrovert. I do not get social energy by being alone, like an introvert does, and I have problems talking with new people and even with friends prefer a back seat in the conversation.

Most people seem to fit into more clear buckets, if you believe the marketing, but that doesn't make the buckets the definition.