Sugarcane is the world's largest crop. It grows in the tropical and subtropical regions of the world, and its harvest provides 80% of the world's sugar. In the United States, most of the commercially available sugar is refined, but in Latin America, unrefined cane sugar is widely available (and much less expensive than refined sugar).
The sugarcane plant is in the grass family, and its large stalks contain a sugary liquid that can be extracted and boiled down in a relatively low tech process. The liquid from the mashed and shredded sugar cane stalks is boiled until it becomes a thick syrup, which is poured into molds. The sugar crystallizes as it cools and turns into a firm, brown, solid block (or cone, depending on the shape of the mold) of molasses-flavored compressed sugar crystals. The remnants of the sugar cane stalks are often used to fuel the fires that boil the syrup.
(Watch an interesting video that shows the entire process from harvesting the sugarcane to un-molding the finished product in rural Colombia - with children and donkeys helping out - here).
The resulting product has different names in different parts of South America. Panela is probably the most universally recognized name for "dehydrated cane juice." In the Andes, it is known as chancaca, and it is an important ingredient in many dishes, like the fragrant syrup for the pumpkin doughnuts called picarones. In Brazil, panela is called rapadura. In Venezuela, it's known as papelón, and in Mexico it's piloncillo.
Panela has a rich, full-bodied taste, somewhat similar to molasses, but a bit milder. (Molasses also comes from sugar cane - a more concentrated by-product that is produced when refined sugar crystals are extracted from the cane liquid - which is why a mild molasses flavor remains in the unrefined cane sugar). The sugar crystals in panela melt on your tongue, a lot like maple sugar candy. You can melt panela with a bit of water to make syrup, or grate it and use it like brown sugar. It's delicious as a sweetener for coffee and tea and can be an excellent addition in loaves of bread and sweets. Unrefined cane sugar is also thought to contain beneficial nutrients which are lost when it is processed into refined sugar.