[fsckboy]

probably best to understand the way people use the term as a risk spectrum, from riskless arbitrage where there is no window for losing money, through say a real estate deal where you find a seller at a good price, and you find a buyer at the market price, and you insert yourself in the middle (a perfect houseflip) even though you don't have the capital to suffer the loss if things get screwed up, to an antique shop that buys on speculation and sells to reliable clients. A pawn shop is arbitrage too.

generally people mean by arbitrage that you enter into a transaction having both a seller and a buyer in mind, or you have two liquid markets with different prices.