The weight and series identifier, where "300" refers to the specific design style and "40" typically indicates the thickness/weight.
The font (often stylized as YD Iygo 340) is part of the "Iygo" series from the South Korean foundry YDType (Yoon Design Group). It is a decorative sans-serif that blends traditional Korean typographic sensibilities with a modern, artistic flair. Visual Aesthetic and Style ydiygo340 font