What makes Invisible by U2 notable?

'Invisible' debuted during the Super Bowl XLVIII commercial break, generating immediate buzz and controversy over its release strategy. It was notable for being available for free on iTunes for a limited time, showcasing U2's innovative approach to music distribution and directly engaging with listeners. Released in 2014, 'Invisible' marked U2's return after the ambitious but commercially mixed 'No Line on the Horizon' (2009). This single was part of their efforts to reinvigorate their sound and connect with new audiences, particularly through a unique partnership with (RED) for charity. It set the stage for their subsequent album, 'Songs of Innocence'.