The act of turning someone or yourself into a
sissy, often via sissy hypno, a chastity cage, and wearing feminine clothing.
Being a
sissy isn't the same as being a trans
woman, as sissification is done as a fetish, and isn't the same as transitioning, though trans sissies do exist.
Sissification is mostly done in femdom relationships and is often combined with other things like cuckolding