A ganachakra is a tantric ritual feast which may be offered as a part of a sadhana. In Tibetan Buddhism, it is also known as a tsog or tsok feast (Tib. tshogs kyi 'khor lo), and is performed by Vajrayana practitioners to accumulate merit and purify the sacred commitments (samayas).
Based on the Sanskrit words gana (gathering) and chakra (circle), ganachakra is actually a generic term for a variety of Tantric assemblies or feasts in which practitioners meet to chant mantra, practice various Tantric rituals, and make offerings.
In Tibetan Buddhism, it is traditional to offer a tsog to Padmasambhava on the tenth lunar day and to a form of Dakini such as Yeshe Tsogyal or Vajrayogini on the twenty-fifth lunar day. Generally, participants are required by their samaya (vow) to partake of a eucharist of meat and alcohol. This ritual derives in part from the Hindu tantric panchamakara or "five Ms": Madya (wine), Mamsa (meat), Matsya (fish), Mudra (rice or grain), and Maithuna (coition).