focal infectionn. A bacterial infection localized in a specific part of the body, such as the tonsils, that may spread to another part of the body.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.focal infection n (Pathology) a bacterial infection limited to a specific part of the body, such as the tonsils or a gland Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014