Made throughout Italy in many different ways, although the most elaborate version is probably bollito misto alla piemontese, once a favourite of Italy's first king, Vittorio Emmanuele.
It features seven kinds of meat: beef (shoulder) veal (breast, tongue and head), a chicken, and pork (cotechino) boiled with seven vegetables (two onion, three ribs of celery, two carrots) and served with seven sauces, usually mostarda d'uva, avije, bagnet vert, bagnet ross, grain mustard (senape), cognà, and horseradish mixed with yogurt.
Bollito misto alla triestina is all pork: smoked pork, cotechino, and würstel, served with cumin seed, sauerkraut, mustard and horseradish.
Bollito by itself nearly always means boiled beef.
Image by Choctaw ridge, Creative Commons License