The word 脱胎换骨 is formed through the sequential combination of four characters: 脱 (to shed), 胎 (womb), 换 (to change), and 骨 (bones). Literally, it means "to shed the womb and change bones", directly constructing a metaphor from Taoist alchemy for a profound personal transformation, where the old self is completely abandoned and a new one is forged.