Autoeroticism
Autoeroticism essentially describes when sexual pleasure or gratification is achieved by one's self instead of through external sources (such as another person). Autoeroticism is used in regards to a few different concepts which all involve sexuality and sexual practices performed alone.
The most common example is masturbation which is sexual stimulation that a person gives themselves. Autoeroticism was used in the past to describe the sexual arousal that occurred during sleep which is a normal occurrence during some sleep stages but this usage of the term has fallen out of favor. Sometimes autoeroticism is used in regards to individuals who are sexually aroused by their own body. Also referred to as autosexuals, these individuals are aroused by themselves and may engage in 'mirror sex' or masturbate to photographs of themselves. This differs from the common form of masturbation in which a person is thinking of another person or their sexual fantasies.