Siddha (Tamil 'Great thinker/wise man', Sanskrit, "perfected one") is a term that is used widely in Indian religions and culture. It means "one who is accomplished". It refers to perfected masters who have achieved a high degree of physical as well as spiritual perfection or enlightenment. In Jainism, the term is used to refer the liberated souls. Siddha may also refer to one who has attained a siddhi, paranormal capabilities.
Siddhas may broadly refer to siddhars, naths, ascetics, sadhus, or yogis because they all practice sādhanā.
The Svetasvatara (II.12) presupposes a 'Siddha body.
In Jainism, the term siddha is used to refer the liberated souls who have destroyed all karmas and have obtained moksha. They are free from the transmigratory cycle of birth and death (saṃsāra) and are above Arihantas (omniscient beings). Siddhas do not have a body; they are soul in its purest form. They reside in the Siddhashila, which is situated at the top of the Universe. They are formless and have no passions and therefore are free from all temptations. They do not have any karmas and they do not collect any new karmas.
According to Jains, Siddhas have eight specific characteristics or qualities. Ancient Tamil Jain Classic 'Choodamani Nigandu' describes the eight characteristics in a poem, which is given below.
"கடையிலா ஞானத்தோடு காட்சி வீரியமே இன்ப
மிடையுறு நாமமின்மை விதித்த கோத்திரங்களின்மை
அடைவிலா ஆயுஇன்மை அந்தராயங்கள் இன்மை
உடையவன் யாவன் மற்று இவ்வுலகினுக்கு இறைவனாமே"