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