Payday was the day when individuals were given their salary by their employer.
Payday at Quark's happened weekly. According to Quark, payday was supposed to be "a time of joy", which led him to question Rom's long face in 2370. When Rom explained that he felt it was unfair for him to receive one to every six of Quark's latinum, Quark changed it to one for every seven. (DS9: "The Homecoming")
Quark's point of view depended on whether he was being paid or paying an employee, as he later remarked when a dabo girl asked for more latinum, "I hate payday." (DS9: "The Collaborator")