A bit shorter than long-tail but longer than traditional bikes, a midtail could "fit into more people's lives" according to Bike Shop Girl. They are easier to store and find parking, fit on a bus rack or on a car bike hitch rack.
The category could include bikes like the Workcycles FR8 and the Kona MinUTE designed with large racks but shorter wheelbases. One of the most popular now is the Tern GSD/HSD, Yuba Boda Boda/Kombi, Salsa Blackborow (a cargo fat bike) and the Xtracycle RFA (again according to Bike Shop Girl).