The
physical act of pulling a
chair over to a
table of some sort, and sitting down in said chair at said table. In yet another
stunning display of
forethought, the
English language has once again misrepresented something: to pull something up implies that 1. you are above that thing, and 2. that it moves in an upward direction. When you "pull up a chair", niether of these conditions are met.
This is also a phrase that carries pretty much the same meaning as "come join us", used often by a group inviting someone they know to join in the
food,
conversation,
game, or whatever. Variations include "pull up a patch of
carpet" or "pull up a
piece of
floor" when the group is chairless.