Terma (; "hidden treasure") are various forms of hidden teachings that are key to Vajrayana and Tibetan Buddhist and Bon spiritual traditions. In the Vajrayana Nyingma school tradition, two lineages occur: an oral kama lineage and a revealed terma lineage. Tradition holds that terma teachings were originally esoterically hidden by eighth-century Vajrayana masters Padmasambhava and Yeshe Tsogyal, to be discovered at auspicious times by treasure revealers known as tertöns. As such, terma represent a tradition of continuous revelation in Vajrayana and Tibetan Buddhism. Tradition Tradition holds that terma may be a physical object such as a text or ritual implement that is buried in the ground, hidden in a rock or crystal, secreted in a herb, or a tree, hidden in water, or hidden in the sky or in space. Though a literal understanding of terma is "hidden treasure", and sometimes refers to objects that are hidden away, the teachings associated should be understood as being concealed within the mind of the guru — that is, the true place of concealment is in the tertön's nature or essence of mind. If the concealed or encoded teaching or object is a text, it is often written in dakini script, a non-human type of code or writing that only a tertön can decipher. Fremantle states: In this way, one may see the tradition of terma and tertön as analogous to that of inspiration and providing a legitimate cultural forum to ensure continuation of tantric tradition, and ensuring Tibetan Buddhism's and Bön's continued relevancy in an evolving world. The terma tradition is particularly prevalent in, and significant to, the Nyingma lineage. Two of the most famous 20th-century tertöns, Jigdral Yeshe Dorje (2nd Dudjom Rinpoche) and Dilgo Khyentse, were Nyingmapa. Tertön are also prevalent in Bön traditions and a few tertön have been Kagyupa. Padmasambhava and Yeshe Tsogyal and principal students secreted away and hid religious texts, ritual objects, relics, et cetera, to be discovered when conditions were ripe for the revelation of their contents. The hidden teachings also secured and protected Buddhism during the time of persecution under Langdarma. Some of these terma have been rediscovered and special terma lineages established throughout Tibet as a result. Out of this activity developed, especially within the Nyingma tradition, two ways of dharma transmission: the so-called "long oral transmission" from teacher to student in unbroken disciplic lineages, and the "short transmission" of terma. The foremost revealers