Cinnamon (alt. Light) is the name of a very light degree roast of coffee beans. In this roast, the beans barely enter first crack, resulting in a relatively dry bean with a light brown color. The internal temperature of the coffee beans will not reach 400 degrees. Coffee brewed from a cinnamon roast often has a sour taste, regardless of origin. This roast is rarely used outside of low cost, commercial coffees. A batch of coffee roasted to such a light degree will result in a larger amount of brewable (and saleable) coffee, as the batch will lose less weight from loss of moisture.
Robusta vs Arabic
Light roasting is not well suited to Robusta beans. Its strong flavor is not well developed and its innate bitterness is pronounced. Instead Robustas are better dark roasted, and are often ground as Espresso. One consideration of roasting darker is the caffeine lost during the roasting process, however Robusta's high caffeine content means it has caffeine to spare.
Arabica beans on the other hand, depending varietal region of the World, can actually benefit from being a lighter roast, if the beans are of high quality and properly roasted. Ethiopian and some Island coffees will be brighter and can retain much more complex flavors of the coffee fruit. Ethiopian Harrar even when raw can smell of blueberries with some citrus coming through as well.
Contrary to City and French roasts (where roasting temperatures can be set to 500F), Cinnamon is best roasted longer and at temperatures starting as low as 300F. This additional time gives the acids and CO2 gases a greater chance to be released. In general, the longer the roast and the lower the starting temperature the better a Cinnamon Roast will be.
By gradually raising the temperature to 400F, the beans won't start first crack too early which can result in them tasting somewhat sour and acidic. Beans can roast well into the first crack this way and still leave a good tasting light roast. With some beans (like Harrar) this process can produce somewhat lively and fruity essences, almost blueberry like and sometimes with hints of nutty complexity.
Many roasters (e.g. Starbucks) are so geared toward darker roasts, that they miss out completely on the these light roasted coffees by setting temperatures too high. This starts the first crack prematurely and results in the sour taste described above.
Note that there is a baking method that produces an even lighter bean called White Coffee.