Filo, also spelled "phyllo," refers to tissue-thin sheets of flour-and-water dough, generally measuring 10 by 14 inches (25 by 35 cm), used as wrappers for savory or sweet fillings. The name derives from the Greek word for "leaf." Sold fresh or frozen, the pastry sheets must be separated and handled carefully to avoid tearing. Be sure to thaw frozen filo in the refrigerator before use. When working with filo, keep those sheets you are not handling at the moment well covered to prevent them from drying out.