The word "chorizo" refers to two rather different pork sausages: Spanish chorizo is a hard, dry-cured sausage spiced with pimentón, and garlic. Since it's cured, it's ready to eat without further cooking, and it adds a meaty note to stews, pastas, and eggs. Mexican chorizo is a fresh sausage, often sold in bulk rather than in links.
Don’t substitute Spanish chorizo for Mexican or vice-versa. A better substitute for Spanish chorizo is another spicy dry-cured sausage; for Mexican, try hot Italian sausage.
Confused whether you're buying Spanish or Mexican chorizo? Note its position in the store. If it's in the cheese or deli case, it's probably cured, ready-to-eat Spanish chorizo. If it's in the meat case, it's probably meant to be cooked. If there are cooking instructions on the label, it's likely that it shouldn't be eaten raw.