Too many activities or undertakings at once. For example, Bill's got too many irons in the fire to cope with moving this year. This expression originally referred to the blacksmith heating too many irons at once and therefore spoiling some in the forging. [Mid-1500s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.