In Hinduism, an astra (Sanskrit: अस्त्र) was a supernatural weapon, presided over by a specific deity. Later it came to denote any weapon which was used by releasing it from one's hand (e.g. an arrow, compared to keeping it one's hand e.g. a sword [shastra]).
Astra (weapon) Wikipedia
The bearer of the weapon is called Astradhari (Sanskrit: अस्त्रधारी).
To summon or use an astra required knowledge of a specific incantation/invocation, when armed. The deity invoked would then endow the weapon making it impossible to counter through regular means. Specific conditions existed involving the usage of astras, the violation of which could be fatal. Because of the power involved, the knowledge involving an astra was passed in the Guru-shishya tradition from a Guru (teacher) to a Shishya (pupil) by word of mouth alone, and only following the establishment of the student's character. Certain astras had to be handed down from the deity involved directly, knowledge of the incantation being insufficient.
Astras come into importance mainly in the Ramayana and Mahabharata, where they are used in the great battles described in each epic. They are depicted as used by archers such as Parashurama, Rama, Lakshman, Indrajit (Meghnad), Ravana, Bhishma, Drona, Karna, Ashwatthaman, Arjuna and other warriors.
The divya astras were generally invoked into arrows, although they could potentially be used with anything. Ashwatthaman invoked Brahmashirsha astra using a blade of grass as his weapon.
Indrajit (Meghnad) the son of Ravana, Lord Parashurama and Karna are believed to be the only humans who ever possessed the three ultimate weapons of the trinity. At a very young age, Indrajit (Meghnada) became the possessor of several supreme celestial weapons, including Brahmanda astra, Pashupatastra and Vaishnavastra, under the guidance of Shukracharya, the Guru of the Daityas (demons). Shukracharya was a disciple of Lord Shiva.