This is the term used for salesfolks who actually put their meat on the street and work for pure goddamn take 'em or leave 'em commissions. No salary. No guarantees. Just sweet, sweet percentages. They usually started out the gig on a draw against commissions.
The distinction is necessary in order to differentiate these folks from inside salesfolks. These are the folks who earn a salary +plus+ commissions, such as retail sales.
Many inside salesfolks gave up a shot at the outside sales world due to the uncertainty of living on straight commissions. Many of them fell prey to call reluctance.
A typical comment you might hear from a successful outside salesperson to describe a buddy of his who gave up trying to do this and took a job at some place like JC Penney's?
"He couldn't sell pussy on a Troop Train."
A typical comment you might hear from the guy who's working at JC Penney's about his friend?
"That son of a bitch is obsessed with money."