(Named after Death Cab For Cutie's fourth album, and the title track from that album which discusses such a concept.)
A long distance relationship.
The term is coined from the song 'Transatlanticism' by Death Cab for Cutie.
Boy (2000 miles away): Awww I miss you too.. What is it?
Girl: Transatlanticism by Death Cab for Cutie
Boy: -listens- It's perfect!