(“initiation”) The name is claimed to be derived from the verb dis, which means "to point out," and refers to a religious initiation including the receipt of hidden religious teachings.
The teenage religious initiation known as upanayana, the ritualized "second birth" given on young males from the three "twice-born" groups—that is, brahmin (priestly), kshatriya (martial), or vaishya—has a distinct meaning than diksha (mercantile).
Both are religious initiations that include the development of new abilities and rights.
However, diksha is a religious initiation in which the novice receives hidden knowledge from a religious instructor (guru), generally in the form of spoken syllables known as mantras.
Unlike upanayana, which occurs when a guy is adolescent, the timing of diksha is determined by a person's desire and preparation rather than their physical age.
Diksha is a particularly significant idea in tantric ritual, as such customized initiations are the means of passing along the heritage from master to pupil.
You may also want to read more about Hinduism here.
Be sure to check out my writings on religion here.