Polycubes are made from cubes that are glued face-to-face without overlap.
In polycube puzzles the player is usually presented with a set of such polycubes and he has the task to use then to assemble them to a certain shape.
Sometimes (especially when polycube puzzles are played on the computer) the cubes will be represented by other tokens.
... the Amazon, the largest river in the world by volume, the Parana[?] with its impressive Iguaçu[?] falls, the Rio Negro, São Francisco[?], Xingu, Madeira and the Tapajós[?] ...