Mojo is a citrus-based marinade. I think it's mostly Cuban, but I think that you find it in Latin and Caribbean cuisines (I could be wrong about that though).
If you do a search for it on Google, you'll find a lot of variations on it. It works well for meat because the acid in the citrus helps tenderize the meat (although you need to marinate for a few hours for it to have any actual tenderizing effect). It's a distant cousin to the marinade you'd use for ceviche. The main difference is that it's usually heavily spiced. So it's almost like a cross between a ceviche marinade and a jerk seasoning without the cinnamon and nutmeg. It's more cumin based.