The pasilla chilli, or chilli negro is a dried chilaca chili pepper. It has a rich smoky and earthy flavour, it is used in mole, other stews, salsas and adobo sauces. It can be used to add low to moderate heat to your dish, with a Scoville heat rating (SHU) of 1500-2500 it is not overly spicy.
Pasilla chillies are part of the Holy Trinity of Mexican chillies used to make delicious mole. The other two are Ancho Chilies and >Mulato chilies.