A merger was the legal union of two previously unrelated businesses.
In 2371, Quark discussed mergers and other financial matters while attempting to prove D'Ghor's crimes, much to Gowron's annoyance. He cut the Ferengi off and asked D'Ghor to answer to his allegations. (DS9: "The House of Quark")
In 2374, Quark compared Odo's potential romantic relationship with Kira Nerys to a merger, saying he'd had plenty of time since her and Shakaar's breakup to arrange it. (DS9: "His Way")