A term with multiple meanings, one is benign, which gives cover to the more malignant definition.

At its best, "Barcon" is the informal gathering of authors and fans in the hotel bar outside of schedule programming to continue conversations, see friends, and have drinks.

The more negative context is used by those who want to take advantage of a convention's space and the people it brings in, but don't want to pay to attend the con. See, also, ghost.