The koru (Maori for "loop") is a spiral shape based on the shape of a new unfurling silver fern frond and symbolizing new life, growth, strength and peace. It is an integral symbol in Maori art, carving and tattoos. The circular shape of the koru helps to convey the idea of perpetual movement while the inner coil suggests a return to the point of origin. Koru is the integral central motif of symbolic, seemingly-abstract kowhaiwhai designs, traditionally used to decorate Maori wharenui (meeting houses). There are numerous semi-formal designs, representing different features of the natural world. Koru can also refer to bone carvings. Those generally take the shape of the uncurling fern frond. When bone is worn on the skin, it changes colour as oil is absorbed. Maori took this to symbolise that the spirit of the person was inhabiting the pendant. When someone gives a pendant to someone else, it is the custom that they wear it for a time so that part of their spirit is given as well.