In my perspective you perform on a daily basis, even if you aren't an actor/actress.
(You have different characters, in a sense of behaviour and language.)
Everyday you interact with different people, you perform differently to those you have known for a long period of time, you have your own way of performing in front of them; you wouldn't act the same way that you do with your friends with your family. As an example, when I am with my family I don't swear and avoid being rude, simply because its just respectful (I know how to act around them in a sense). Whereas, with friends, I will swear, make rude jokes, because I know that I am allowed to act in that way.
Many would say that if you don't have an audience, do you really have a performance? I would say, well of course, you, as a person, are still acting, the world is your audience. An audience doesn't need an expensive seat, to be seen as your audience, your audience could be as simple as someone walking down the street and glancing at you.
However, thats just how I see it...