traditionally Mul yut is malted barely syrup. A semi by product of making a naturally sweet Gam ju or Shi keh (korean rice and malt puch)
Mul yut is added to foods and certain ban chan towards the end of the cooking or preparing process to give the dish a shine or to give sauces a richer texture. You will see many korean recipes with Mul yut as an ingredient.
today, Mul yut is made purely from corn starch. The best substitute is corn syrup, not honey. honey is too sweet and it adds unwanted flavor and it also does not give the dish any shine. try to look for the syrups with minimal ingredients in it.