In Hinduism, in the Vedas, dīkṣa was a necessary prerequisite for the soma sacrifice undergone by the sacrificer (yajamāna) and his wife, involving asceticism (tapas) and fasting. In the Upaniṣads, initiation into an ascetic life involves undergoing hunger, thirst, and abstention from all pleasure (Chandogya Upaniṣad 3. 17. 2). The importance of dīkṣa carries on into classical and medieval Hinduism where subtraditions within the central traditions of Vaiṣṇavism, Śaivism, and Tantrism all required dīkṣa.
There are different kinds and various stages of dīkṣa particularly in Tantrism where the utmost secrecy is maintained. In Śaivism the ‘collective’ (samaya) and ‘particular’ (viśeṣa) initiations give access to the cult of Śiva.
In Jainism, dīkṣa is the ceremony whereby a person passes from lay status to being an ascetic.
"Dīkṣa." The Concise Oxford Dictionary of World Religions. . Encyclopedia.com. (December 17, 2018). https://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/diksa
"Dīkṣa." The Concise Oxford Dictionary of World Religions. . Retrieved December 17, 2018 from Encyclopedia.com: https://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/diksa