A KUSH Collection is a group of "KUSH" objects. Objects that are "KUSH" are comfortable and luxurious, hence a KUSH Collection is a group of comfortable and luxurious objects.
"Kush" is also used to describe a feeling or a person, as in "that person is really KUSH."
"That new silicon washed Hooded sweatshirt I bought at Fred Segal is so KUSH. Fred Segal has a great kush collection of clothes."
"That girl we met at the bar tonight was so KUSH. She bought us each a drink and smoked a joint with us in her Range Rover!"
"That is a KUSH Collection of girls! They are all beautiful, confident and really friendly!"