The ceremony marking a Ferengi male's passage to adulthood, after which custom requires him to buy an apprenticeship with a mentor of his own choosing.
The Attainment Ceremony is the Ferengi coming of age. A male who has completed it is an adult. By tradition he must then pick a mentor and pay for the privilege of being apprenticed to them.
It lies behind the secondary story of Heart of Stone in 2371. Fresh from his ceremony, Nog comes to Benjamin Sisko with a bag of latinum and asks to become his apprentice, because he wants to join Starfleet. Sisko assumes a trick and sets him to inventorying a cargo bay, which Nog does quickly and thoroughly.
Pressed for his real reason, Nog says he does not want to end up like his father Rom, a talented engineer wasted because he has no head for business. Sisko agrees to recommend him to Starfleet Academy, and Nog goes on to become the first Ferengi in Starfleet.