The document discusses different types of obsolescence, which is when a product is no longer useful due to technological changes or falling out of fashion. It describes technical obsolescence when new technologies make old ones obsolete, planned obsolescence when manufacturers deliberately design products to become obsolete to drive repeat purchases, style obsolescence when products go out of style, and postponement obsolescence when improvements are not implemented in some products. Obsolescence can occur even if products still function when supporting technologies or parts are no longer available.