Whirl (drilling) : A detrimental condition where a bit bites into a part of the hole off center and forms a pivot point that creates impact of the bit and some of the string with the borehole wall
George E. King Engineering, 5000 Oilfield Terms: A Glossary of Petroleum Engineering Terms, Abbreviations and Acronyms, US 2010. http://gekengineering.com/Downloads/Free_Downloads /Glossary_of_Petroleum_Engineering_Terms_25_August _2010.pdf, (Oil - Amer) {593}