This thread really got me thinking.
To me, extroversion means that I seem to constantly need something going, usually multiple stimuli at once. At work, I'll listen to music and drink tea while swapping back and forth between multiple projects, all the while welcoming interruptions from emails or coworkers stopping by.. focusing on one task is admittedly sometimes difficult, but I can juggle multiple tasks with ease. When I'm at home, I've either got a chat window going while doing other things, or I'm on the phone, or I've got people over. Out and about in grocery stores and the like, I'm always looking around and observing my surroundings and other people. Socially, I generally can't help but contribute to conversations when I feel that I actually can.
Above all, I actively try to learn from other people. As others have said, they bring out parts of me that I may not have seen before.. but then those parts also often stick with me to some degree once they're brought out.
Well, in the context of I/E:
Take the ENFP and INFP, for example. I say both lead with Intuition, which is an intersection of Ni and Ne as Jung conceived them (Parts of both; All of neither), and both have Feeling as the 2nd, or support function.
I/E will affect behavior, and must also affect use of N,S,T, and F. So, perhaps the INFP does use "Ni" more than "Ne," and perhaps not, but I propose it's just as likely they use "Fi" more than "Fe" also, and so on.
And, in this context (which I like!), I suppose extroversion can also mean that my singular Thinking function is oriented toward planning, organizing, systematizing, and otherwise logically processing the
outside world most of the time, because that's largely where my attention is.