Diksha is a special process for removing evil taints and initiating pupil with powers and siddhis.

Kinds of Dikshas are:
Chakshusi by mere glance
Sparsa by touching the head.
Vacha by words blessing.
Manasi mentally blessing.
Sastri by teaching sastras.
Yoga is Guru entering into the pupil’s mind inwardly.
Howtri Kriyavati performing homas [...]

The Kula Moolavatara Kalpa Sutra Teeka Gata Kulagama mentions six classes of Gurus in regular gradation. They are;
Preraka One who just starts the pupil Suchaka One who indicates and carries further Vachaka One who regularly teaches and coaches Darscaka One who points out the way and goal to the pupil. Sikshaka One who regularly teaches [...]