The member of a group that goes out to get needed supplies, i.e. alchohol,
food,
ice, condoms,
cigarettes, etc.
This person's effort acts as a deduction against share tax, and he/she is usually the initiator of insies.
Mary: We're outta smokes and
beer. I've only got $5 but I'll be runner if anyone wants insies.
Everyone: Okay
Mary: I need your share tax.
Joe: Here's another $10.
Jim: I'll give another $10
Jane: I'm giving $20 to cover the rest of Mary's share 'cause she's the runner.