Prajna (प्रज्ञा) is the Sanskrit word for "wisdom" — specifically transcendent wisdom that perceives ultimate reality. The third of the six paramitas (perfections) of Mahayana Buddhism — embodied by Prajnaparamita, the "Mother of all Buddhas."
The Heart Sutra and Diamond Sutra are her core teachings.
Prajna reduces to one — the number of Buddhist wisdom.