Is there a difference between masturbation and self-pleasure, and what is religiously prohibited, and is mere fantasizing about engaging in sexual intercourse without touching the organs considered masturbation?

Masturbation is the seeking of semen expulsion, which includes self-stimulation by hand or imagination and other means. As for "al-adah al-sirriyyah" (the secret habit), it is a term coined by people, by which they specifically mean masturbation by hand, making masturbation a broader term than "al-adah al-sirriyyah". "Al-adah al-sirriyyah" in this sense is forbidden, and likewise, for an unmarried person to imagine intercourse and its preliminaries with someone unlawful to him, and to persist in such thoughts, is forbidden.