Vimalaprabha means 'Stainless Light Commentary', or 'Dri-med ‘od' (in Tibetan), it is a commentary to the Kalachakra

Kalachakra

Kalachakra is a Sanskrit term used in Tantric Buddhism that literally means "time-wheel" or "time-cycles".The spelling Kalacakra is also correct....

 tantra, more specifically, the Laghutantra or Abridged Kalachakra Tantra from Shambhala King

Kings of Shambhala

In the Indo-Tibetan Vajrayana Buddhist tradition, there are thirty-two Kings of Shambhala, a mythical kingdom.The first notable king of Shambhala, King Suchandra , was the one who requested teaching from the Buddha. In response to his request, the Buddha gave the first Kalachakra root tantra...

 Manjushri-Yashas. The Vimalaprabha was written by Shambhala

Shambhala

In Tibetan Buddhist tradition, Shambhala or Shangri-la is a mythical kingdom hidden somewhere in Inner Asia...

 King Pundarika.

This Vimalaprabha commentary, together with the Laghutantra form the basis of the Kalachakra practice as it is currently known and practiced in Tibetan Buddhism

Tibetan Buddhism

Tibetan Buddhism is the body of Buddhist religious doctrine and institutions characteristic of Tibet and certain regions of the Himalayas, including northern Nepal, Bhutan, and India . It is the state religion of Bhutan...

, as part of the Vajrayana

Vajrayana

Vajrayāna Buddhism is also known as Tantric Buddhism, Tantrayāna, Mantrayāna, Secret Mantra, Esoteric Buddhism and the Diamond Vehicle...

practices.