The Franks were originally a germanic tribe from the lower Rhine, on the edge of the Roman Empire. During the 5th century, they expanded and converted to Christianity, laying the foundations for and eventually transitioning into the Merovingian kingdoms, which in turn morphed into the Carolingian empire under Charlemagne, controlling much of western Europe.

Charlemagne's empire ultimately collapsed under his grandsons. The "Frankish" legacy was mostly claimed by France (clue in the name, there), but Carolingian influence extended from the Pyrenees to what's now Croatia and from the shores of the North Sea to Rome.

By the time of Urban II, "Franks" was pretty much just a generic term for "western European." Generally, "Franks" and "Latins" were used interchangeably to refer to Latin Christians (i.e. Catholics, i.e. most folks from Western and Central Europe at the time), regardless of whether the lands they were from had ever been part of Charlemagne's empire.

Beyond western Europe, among Eastern Orthodox (like the Byzantine Empire) and Muslim followers, "Frank" was used as a synonym for anyone from Western or Central Europe, especially Latin Christians. The medieval Persians and the Ottomans called Europe "Frangistan" (meaning "land of the Franks).

Even the Mongols called Europeans "Franks" and thanks to eastern trade, the Chinese called Europeans (particularly the Portuguese who sailed there in the 16th century) "Folangji" or "Fah-lan-ki", which translate to -- you guessed it, "Franks". Basically, up until modern times some cognate of "Frank" was used by practically everyone from the Middle east to Malaysia to refer to all of Europe and Europeans.