What is Tantra? The process of transforming [latent divinity] into the Supreme Divinity is known as Tantra sádhaná. The sleeping divinity in animality is termed, in the language of spiritual aspirants, the kulakuńďalinii. So we find that actually the spirit of Tantra sádhaná lies in infusing a [vibration] in the kulakuńďalinii and pushing her up towards the spiritual goal.
The significance of the term tantra is "liberation from bondage [the bondage of dullness, or staticity]". The letter ta is the seed [sound] of dullness. And the root verb trae suffixed by da becomes tra, which means "that which liberates" – so the spiritual practice which liberates the aspirant from the dullness or animality of the static force and expands the aspirant's [spiritual] self is Tantra sádhaná. So there cannot be any spiritual practice without Tantra. Tantra is sádhaná.
Spiritual practice means practice for expansion, and this expansion is nothing but a liberation from the bondage of all sorts of dullness [or staticity]. A person who, irrespective of caste, creed or religion, aspires for spiritual expansion or does something concrete, is a Tantric. Tantra in itself is neither a religion or an ism. Tantra is a fundamental spiritual science. So wherever there is any spiritual practice it should be taken for granted that it stands on the Tantric cult. Where there is no spiritual practice, where people pray to God for the fullfilment of narrow worldly desires, where people's only slogan is "Give us this and give us that" – only there do we find that Tantra is discouraged.
The main characteristic of Tantra is that it represents human vigour. It represents a pactless fight. Where there is no fight there is no sádhaná. Under such circumstances Tantra cannot be there, where there is no sádhaná, no fight. It is an impossibility to conquer a crude idea and to replace it by a subtle idea without a fight. It is not at all possible without sádhaná. Hence, Tantra is not only a fight, it is an all-round fight. It is not only an external or internal fight, it is simultaneously both.
Shrii Shrii Ánandamúrti
Discourses on Tantra, volume II
"Tantra and its Effect on Society"