The difference between wicker and rattan is the distinction between a product versus a process. Rattan is a type of wood with a vertical grain that is often used to make woven furniture items. An item made with a particular weaving style — whatever material is used — is called wicker.
In its original form, rattan is a relative of the tropical palm tree. It starts to grow upwards like a tree, but then bends back to the ground and snakes through the rain forest like a vine. After a few years of growth, the vines are cut into 12 to 18 foot (about 3.7 to 5.5 meters) sections and hauled away for drying. Furniture companies to treat the wood and ship it out to large furniture manufacturing plants in China.
Rattan is considered to be one of the strongest woods available, since its grain grows vertically instead of forming the concentric rings of most other hardwoods. The straight wood is usually steamed and then bent into the desired shape through the use of specialized shapers. Once dried, it will retain its shape forever. These poles are often used to form the frames of what will become rattan or wicker furniture.