What is the difference between Char Siu and chashu?

Could you please elaborate on the key distinctions between Char Siu and chashu? Are there any notable differences in their preparation methods, ingredients, or cultural origins? Additionally, how do their flavors and textures compare, and are there any specific dishes or cuisines where one is more commonly used than the other? Understanding these nuances would greatly enhance my appreciation for these two delicious meats.