Maithuna is a Sanskrit term used in Tantra, which is most often translated as sexual union within a ritual. Maithuna refers to the coming together of god and goddess with the acknowledgement that everything is sacred, from food to acts of lovemaking. It uses physical unification for the purpose of creating spiritual unification.
Since Maithuna is practiced as a spiritual ceremony, there is an acknowledgement and honoring of a divine being. However, in Tantra, this deity is acknowledged and honored in your partner, rather than as an intellectual concept or spiritual ideal. Tantra encourages lovers to see the divinity in each other.