1. [informal] A situation characterized by repeatedly dealing with recurring problems as soon as they appear, often in a random manner
   "Fixing bugs in the software became a frustrating game of whack-a-mole"
    
2. (trademark Whac-A-Mole) an arcade game in which players use a mallet to hit toy moles that pop up from holes on a board
   "The children spent hours playing whack-a-mole at the arcade"

Encyclopedia: Whack-a-mole