Emu48 Underscore Command?

[MNH]

4:
3:
2:
1: HAPPY_NEW_YEAR_2021
===========================================================
_ Error:
Too Few Arguments

4:
3:
2:
1: ""
===========================================================

Prior to my earliest post today, I was trying to create the above directory. Upon entering the name on the stack, I received the above message. I don't ever remember seeing an underscore command anywhere. Please explain.