Raw sugar is cane sugar which has been minimally processed. The precise definition varies, depending on who you talk to. Adherents to a raw food diet, for example, may have very specific definitions which involve temperature and handling, while others may view any sort of lightly refined sugar as raw sugar. In all cases, raw sugar is the product of the first stage of the cane sugar refining process, and as a result it has some very distinctive characteristics.
Sugarcane is a type of grass which grows in the tropics. People in India and parts of Asia realized that sugarcane was naturally very sweet thousands of years ago, and they started pressing it for the sweet juice and refining the result. Given that raw sugar requires minimal processing, the raw sugar we consume today is probably very similar to that made in India hundreds of years ago. When Europeans started to explore Asia, one of the first products they were introduced to was sugar, and it proved to be a big hit; it was also one of the first crops established in the Caribbean colonies, demonstrating how readily people took to it.
In order to extract regular table sugar from sugarcane, two steps are required. In the first stage, the raw sugar is extracted from the canes, processed to remove major impurities, and then dried. The dried sugarcane juice can be further refined in a second step, which purifies the sugarcane even further, removing the residual molasses and concentrating the sucrose to turn it into light brown, dark brown, and white sugars.
To make sugar, sugarcane is cut and then run through a press to extract the juice. Once the juice has been extracted, it is boiled and then cooled, allowing it to crystallize. Depending on how it is handled, the sugar may crystallize into a very fine, granular sugar with a high molasses content which can be sold as-is or further refined into brown and white sugars, or it can form large pale golden crystals, which are sold as raw sugar.
Because raw sugar is not heavily refined, it has a higher molasses content than table sugar, which lends the raw sugar a rich, complex flavor. The large granules are also delightfully crunchy, which is why raw sugar is often used as a topping for pastries and various desserts. There are some cautions involved in using raw sugar in cooking, however, as it has a higher moisture content than regular sugar, and this can throw delicate recipes off. It can also dry out, causing it to harden; keeping raw sugar in an airtight container is highly advised.