What is the difference between masturbation, "ada sirriya" (a common euphemism for masturbation), "tafreedh" (a specific type of manual stimulation often translated as "fingering" in a sexual context), or masturbation by one's wife, from the Sharia, physical, and psychological perspectives?

Masturbation is synonymous with self-pleasure (istimna'), which is the expulsion of semen. If it is done by the wife, it is permissible. If it is done by anyone else, it is forbidden. It is permissible for a husband to enjoy his wife in any manner, including masturbation by her hand, as long as it does not lead to something forbidden, such as anal intercourse. As for the physical and psychological harms, one should consult specialists regarding them.