tomatillos means: Small, green, firm, tomatoes. The husk is a thin, paper-like covering that they are wrapped in before being cooked. They add great flavor to sauces thanks to their acidity. (in Cooking Dictionary)
What else does tomatillos mean?
Spanish frescadillas are plum-sized bright green fruits covered in a papery husk. They have an acidic taste and are closely related to tomatoes. It is also a nightshade member; it was eaten originally by the Aztecs. The best replacement for them are small, green tomatoes. Remove the papery husks if you are using fresh. Cans are an acceptable substitute. However, it is important to rinse the cans well after use. (in Cooking Dictionary)