Piloncillo is the Mexican therefore more common (for me anyways) term for hard brown sugar from Latin America. It means "little pylon" or cone since that is the common form it is found in...normally 1 ounce or 8 ounce cones.
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From About.com:
Piloncillo is made from pure, unrefined sugar that is pressed into a cone shape. It tastes very similar to brown sugar with a molasses flavor (even though it does not contain molasses) and you can use it for anything that calls for brown sugar. It's name means "little pylon" because of it's shape. The smaller cones are usually around 1 ounce and the larger ones around 8 ounces. They come in light, "blanco" and dark "oscura."
Some delicious Mexican recipes using piloncillo include Capirotada, a bread pudding and Atole, a sweet, porridge style drink.
If you don't have piloncillo on hand, you can substitute 1 cup of dark brown sugar and 1 tablespoon molasses for each 8 to 9oz cone.
Pronunciation: pee-lon-SEE-yoh
Also Known As: panela
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I was calling Mexican grocery stores asking for "panela" and they kept asking if I wanted cheese.

Turns out "queso panela" is a cheese product so in Mexican neighborhoods it is referred to as "piloncillo" to avoid confusion.
Once I realized this and started asking for piloncillo I found it all over the place for 99 cents a pound so there ya go.
tp (and today's Spanish lesson)