Osa falls when nine of the sixteen Diloggun cowries land mouth up. Like most of the sixteen parent signs, its name carries across directly to the corresponding figure in Ifa divination, part of the shared Yoruba vocabulary that both oracles preserved through the upheaval of the transatlantic slave trade and the long colonial suppression of African religious practice in Cuba.
The parent signs are not, on their own, a complete divinatory system; a working reading combines two throws of the sixteen shells to produce one of the two hundred fifty six compound Odu that carry the tradition's full store of proverbs, myths and prescribed remedies, with Osa serving as one half of whichever compound figure results. That combinatorial structure is what lets a relatively compact physical kit, sixteen shells, generate a divinatory literature broad enough to address the range of situations Lucumi diviners are consulted about. The compound figures and their associated teachings are the closed-practice material proper to initiated diviners and to the person receiving a reading; this entry accordingly limits itself to Osa's place among the sixteen parent signs and the combinatorial logic that governs how they are used together.