A variety of layered pastry that rises when baked (unlike, say, phyllo pastry). Puff pastry is made by putting chilled butter (or lard) between several layers of normal pastry dough, rolling it flat, folding it over, and repeating many times until the final dough consists of hundreds of very thin layers of dough and cold butter. When the dough is baked, the moisture in the butter boils up and the steam causes the dough to rise, resulting in puffy, flaky (and extremely rich and fatty) pastry. It's commonly used for pie crusts, strudels, and sausage rolls. Because it's such a pain in the ass to make, commercial frozen puff pastry - Tenderflake et al - is very popular with the not-a-gourmet-chef crowd.