The Tablets (石板, Sekiban?), also known as Slabs, are key items in Final Fantasy V used to unlock the twelve sealed weapons. Four tablets exist in the world. Hidden in determined points of the world related to the elements, their location is written in the Sealed Book: one lies in the Pyramid of Moore, one lies in the Island Shrine, one lies in the Great Sea Trench, and one lies in the Istory Falls.
Each tablet is associated with some sort of magic; the tablet at the Pyramid of Moore summons Bahamut, the tablet at the Island Shrine allows entry to the Fork Tower where the ultimate spells Holy and Flare can be obtained, the tablet in the Great Sea Trench grants the party the ultimate Time Magic spell Meteor, and the tablet in Istory Falls calls Leviathan from the waterfall.
Only the first tablet has to be acquired to beat the game, but it's advisable to get the second and third ones to get Flare, Holy and Meteor.