Traditionally, when a housewife made bread she would save part of the dough, roll it flat and place it in the oven. Often a schiacciata (literally 'squashed') is something about the same as a focaccia. A proper one has a dimpled texture, made from the baker squashing the dough between her fingers, creating something halfway between bread and pizza. In central Italy they might have only salt, olive oil and rosemary on top (here's a good recipe); in Sicily, they are topped with herbs, onions, olives, cracklings, or lard (strutto).
In Tuscany, they make a plain version and a schiacciata unta (with lardo); two kinds, the schiaccia di Grosseto and the schiaccia pizzicata ('pinched') di Montiano are registered as PAT. Outside of Sicily and Tuscany, commercially sold schiacciata are usually thin and crispy.
Except sometimes in Tuscany, where sciacciata can mean the exact opposite: a sweet, even fluffy bread, as in their aniseed-flavoured schiacciata di Pasqua (other names for this include stiacciata in Livorno and sportellina in San Gimignano). Other Tuscan versions include:
Schiacciata dell’uva or con l'uva: a sweet foccaccia made with red grapes, and usually walnuts and rosemary made during the grape harvest.
Schiacciata Fiorentina: square, sweet, covered with powdered sugar and usually marked with the city's lily symbol.
Images by: gnuf, ideericette