Pretotyping was coined by Alberto Savoia during his time at Google. It refers to the practice of rapid testing to determine the desirability of a solution. Preptotyping differs from prototyping in that the solutions are often "faked" to the end user during testing to mimic the ideal outcome. This allows you to gather real feedback without investing the time to develop and build the working product. The ultimate goal of Pretotyping is to reduce the risks and costs of product development by focusing on making sure you are building the right thing before focusing on building that thing right.
A popular example of Pretotyping was the Palm Pilot. In order to validate the size, shape and usability of the device the founder cut out a block of wood the size and shape of the device and carried with him in his pocket to simulate what carrying the device would be like.