Scalper

Noun

1. One who scalps, or removes the scalp of another.
2. One who scalps tickets to popular entertainment events: buying them in advance and then selling them (e.g. online or just outside the venue of the event), often at inflated prices.

   "We could see three different scalpers moving through the crowd outside the arena, each muttering the characteristic refrain: “Need any tickets?”"

3. One who scalps any other item with limited availability.
4. A gambler who scalps.
5. A person on an open outcry exchange trading floor who buys and sells rapidly for his or her own account, aiming to buy from a seller and a little later sell to a buyer, making a small profit from the difference (roughly the amount of the bid/offer spread, or less).