Merger Arbitrage

What Does Merger Arbitrage Mean?
A hedge fund strategy in which the stocks of two merging companies are simultaneously bought and sold to create a riskless profit.

Investopedia explains Merger Arbitrage
A merger arbitrageur looks at the risk that the merger deal will not close on time, or at all. Because of this slight uncertainty, the target company's stock will typically sell at a discount to the price that the combined company will have when the merger is closed.

A regular portfolio manager may focus only on the profitability of the merged entity. In contrast, merger arbitrageurs care only about the probability of the deal being approved and how long it will take the deal to close.