According to Osho, tantra means expansion as the effortless widening of awareness that remembers our already-present oneness with existence. Nothing is added from outside; when the mind stops roaming, consciousness expands into the crystal-clear herenow, and the feeling of unity flowers. Tantra is simply being totally present so the dream of separation dissolves and our indivisible nature is revealed.
Tantra is just opening your awareness right now so you feel one with everything instead of lost in thoughts.