The term 'so long' is a phrase used to bid farewell to someone. It can be expressed in many different ways, such as 'CIAO' (4 letters), 'ADIEU' (5 letters), 'LATER' (5 letters), 'ADIOS' (5 letters), 'GOODBYE' (7 letters), 'BYE' (3 letters), 'tata' (4 letters), 'imoff' (5 letters), 'seeya' (5 letters), 'byebye' (6 letters), 'byenow' (6 letters), 'seeyou' (6 letters), 'toodleoo' (8 letters), 'imoutahere' (10 letters), 'seeyalater' (10 letters), 'hastalavista' (12 letters), and 'haveaniceday' (12 letters). All of these phrases are used to express the sentiment of saying GOODBYE.