As in butter, oil or lard, or just plain greasy (other words are untuoso or oleoso). Also used for Martedi Grasso—Fat Tuesday or mardi gras. Another word you may see on lists of ingredients is lipidi.
grasso d'anatra: duck fat
Grasso di palma: palm oil
Grasso non saturo: unsaturated fat
Grassi polinsaturi: polyunsaturated fat
Grasso saturo: saturated fat
Grasso trans: trans fat
Grasso vegetale: vegetable fat
Senza grassi: fat free
Image by Dan Perry