Where does “καλοκαιριάτικα” come from?

καλοκαιριάτικα (Greek) comes from Greek καλοκαίρι, from Byzantine Greek καλοκαίριν, from Ancient Greek καλοκαίριον — fine weather.

καλοκαιριάτικα (Greek): in the summertime, in the summer usually with reference to something not appropriate or usual for the season