It means dances in longways (duple minor) formation.
Nowadays the first coupe are usually 'improper', 2s 'proper' so you've got an alternating line of men and women. In all Duple minor dance you start in small circles of 4 (minor sets), and during the first turn of the dance the 1s and 2s change places, starting the next turn with a different couple.

My guess is that Contra, MUC (modern urban contra) and Zesty Contra fill the need for high energy dancing with lots of swinging that E-Ceilidh does here.