According to psychiatristDarold Treffert, almost all savants have prodigious memory which he describes as "very deep, but exceedingly narrow." It is narrow in the sense that savants may exhibit exceptional memory but have difficulty putting it to use. Some individuals with savant syndrome also have a keen sense of priority, which can involve a broad understanding of politics, law, and a conceivably heightened vocabulary.
Savant skills (islands of ability) are usually found in one or more of five major areas: art, musical abilities, calendar calculation, mathematics and spatial skills. The most common kind of autistic savants are the calendrical savants, ‘human calendars’ who can calculate the day of the week with speed and usually with accuracy. Memory feats are the second most common savant skill in a survey.
50% of savants have autism; the other 50% often have some other forms of central nervous system injury or disease. Among autistics, 10% have some form of savant abilities.
No widely accepted cognitive theory explains savants' combination of talent and deficit. It has been suggested that individuals with autism are biased towards detail-focused processing and that this cognitive style predisposes individuals either with or without autism to savant talents. Another hypothesis is that savants hyper-systemize, thereby giving an impression of talent. Hyper-systemizing is an extreme state in the empathizing–systemizing theory that classifies people based on their skills in empathizing with others versus systemizing facts about the external world. Also, the attention to detail of savants is a consequence of enhanced perception or sensory hypersensitivity in these unique individuals. It has also been confirmed that some savants operate by directly accessing low-level, less-processed information that exists in all human brains but is normally unavailable to conscious awareness.
Savant syndrome results from damage to the left anteriortemporal lobe, an area of the brain key in processing sensory input, recognizing objects and forming visual memories. Savant syndrome has been artificially replicated using transcranial magnetic stimulation to temporarily disable this area of the brain. 
There is no agreement about how many people have savant skills. The estimates range from "exceedingly rare" to one in ten people with autism having savant skills in varying degrees. A 2009 British study of 137 parents of autistic children found that 28% believe their offspring met the criteria for a savant skill, defined as a skill or power "at a level that would be unusual even for "normal" people". As many as 50 cases of sudden or acquired savant syndrome have been reported.
Males with savant syndrome outnumber females by roughly 6:1—slightly higher than the sex ratio disparity for autism spectrum disorders, which is 4.3:1.
The term idiot savant (French for "learned idiot" or "knowledgeable idiot") was first used to describe the condition in 1887 by John Langdon Down, who is known for his description of Down syndrome. The term "idiot savant" was later described as a misnomer because not all reported cases fit the definition of idiot, originally used for a person with a very severe intellectual disability. The term autistic savant was also used as a diagnosis for this disorder. Like idiot savant, the term autistic savant also became looked at as a misnomer because only one-half of those who were diagnosed at the time with savant syndrome were autistic. Upon realization of the need for accuracy of diagnosis and dignity towards the individual, the term savant syndrome became widely accepted terminology.
A prodigious savant is someone with a skill level equivalent to or greater than that of a prodigy, regardless of any cognitive disability. The most common trait of prodigious savants is their seemingly limitless mnemonic skills, with many having eidetic or photographic memories. Prodigious savants are extremely rare, with fewer than one hundred noted in more than a century of literature on the subject. Treffert estimates that fewer than fifty or so such individuals are alive today.
Prodigious Godly Savants were mentioned in both The Arabic Infancy Gospel > and The Infancy Gospel of Thomas  which were a lager part of The Apocryphal New Testament, and which describe the Savant life of Jesus as a child. In other religious writings, these gifted individuals were called Godly Savants or Spiritual Geniuses and were described in The Second Coming of Christ by Paramahansa Yogananda. Godly Savant references to Jesus, Shukadeva (compiler of the Vedas and composer of the Mahabharata) and the Hindu Saint Swami Shankara can also be found here. Prodigious Savants were widely written about in India as a part of their spiritual lore and writings in the Bhagavad Gita 
The following are well-known people with savant syndrome, noted for their talent in their identified fields:
^"The Childhood and the Life of James Henry Pullen, the Victorian Idiot Savant (1832–1916)" in "History of paediatrics and child health". Archives of Disease in Childhood88 (90001): 59A. 2003. doi:10.1136/adc.88.suppl_1.A59.