Nice topic! Yes, for us alpinists and hard mountaineers, a Dulfer is a layback. In a crack, hands pull while feet push.
It's one of those magic words that, ages ago, my friend and I looked for in the guidebook, to write possible routes off.
Others were: camino, diedro, pendolo, basically everything bar open, clear slabs.
Other important captions were after routes' sections, like "the human trap", "use the human tower technique", or routes' names like "the oblique death".