A session is what those who attend regularly or organise it decide what it should be as opposed to what a visitor may like or wish it to be. This is often on a de facto basis, of course.

Ideally, for me, it should be a participatory activity involving sharing music with people as opposed to playing or singing AT people. This doesn't exclude singing a solo song or playing a tune on your own but generally people will be expected or encouraged to join in if they can. Of course, they should also have enough good sense and taste to know when it's best to stay out.

Many Irish players believe that a session is a very strict "tune only" affair and always a communal effort. That is fine, of course, and I respect that if I'm there but I believe other arrangements are also possible.