I'm looking at some "e-ticket itinerary/receipt" issued by Korean Air for a flight from the United States to Asia. I read the baggage information section and it says:
Please check the detailed baggage regulations on the Korean Air website. Unregulated baggage may not be transported or may be charged an extra fee. Excess baggage charges can be paid in advance on the website. Items restricted from transportation of consigned baggage. Carry-on baggage Checked Baggage
What's an unregulated baggage?