diksha is a term for initiation.
Hindu Tantrics are organised by preceptorial lineages samprayada where authority comes from the guru and texts only have a secondary importance (Tantra is primarily an oral tradition). Initiation begins the process whereby the sadhaka is transformed into a divinised vessel for embodying the energy of a particular god or goddess. Initiation requires a teacher who has previously been so empowered by diksha, who can 'plant' in the initiate a 'seed' that is the divine essence of deity. This can take many forms, such as a mantra, an image, or the transfer of the guru's own sakti. This transfer can take many forms, ranging from ritual sexual intercourse to food offerings or the exchange of prana by breath, and varies according to particular 'traditions'. Furthermore, initation causes the practitioner to be 'reborn' into the 'familty' of the lineage.