Speck is an English word meaning "fat", attested since the early 17th century. This word also exists in German with the same meaning, but it normally refers to pork fat with or without some meat in it. Normal English use refers to German culinary uses, particularly of smoked or pickled pork belly. In Dutch, spek is a generic term for bacon/lard.
In Italy, Turkey and parts of the English-speaking culinary world, the term "speck" refers to Italian speck, a type of prosciutto, rather than German speck. The term "speck" became part of popular parlance only in the eighteenth century and replaced the older term "bachen", a cognate of "bacon".
There are a number of regional varieties of speck, including:
In Ashkenazi Jewish cuisine, in which bacon is forbidden as a unkosher pork, "speck" commonly refers to the subcutaneous fat on a brisket of beef; it is a particular specialty of delis serving Montreal-style smoked meat, where slices of the fatty cut are served in sandwiches on rye bread with mustard, sometimes in combination with other, leaner cuts.