Siddha
A Siddham in Tamil means "one who is accomplished" and refers to perfected masters who, according to Hindu belief, have transcended the ahamkara (ego or I-maker), have subdued their minds to be subservient to their Awareness, and have transformed their bodies (composed mainly of dense Rajo-tama gunas) into a different kind of body dominated by sattva. This is usually accomplished only by persistent meditation.
According to Jain belief Siddha are liberated souls who have destroyed all the karma bondings. Siddha do not have any kind of body, they are soul at its purest form. They reside in Siddha-shila which is situated at the top of the Universe.
A siddha has also been defined to refer to one who has attained a siddhi. The siddhis as paranormal abilities are considered emergent abilities of an individual that is on the path to siddhahood, and do not define a siddha, who is established in the Pranav or Aum – the spiritual substrate of creation. The siddhi in its pure form means "the attainment of flawless identity with Reality (Brahman); perfection of Spirit."
In the Hindu philosophy of Kashmir Shaivism (Hindu tantra), siddha also refers to a Siddha Guru who can by way of Shaktipat initiate disciples into Yoga.
Read more about Siddha: Siddha or Siddhar (Tamil Tradition ), Siddha in Jainism, Siddha-shila, Siddhashrama, Siddha Sampradaya