The Y2K bug, also known as the Millennium Bug, was a software flaw that sparked global concern in 1999 as the new millennium approached. The issue stemmed from older computers using two digits to represent the year, raising fears of system failures when transitioning from December 31, 1999, to January 1, 2000. This triggered a worldwide scramble for fixes, increasing technological investment and labor focus, impacting productivity and the economy. Proactive measures largely prevented major disruptions.