A loading meter is one metre of trailer length across the full width (2.4 m). A standard trailer has 13.6 LDM. A Euro pallet (120 × 80 cm) takes 0.4 LDM; a block pallet (120 × 100 cm) 0.5 LDM.
Road part loads (LTL) are often priced per loading meter, because floor space is what fills a truck. Stackable pallets can lower the LDM you pay for.
Example: 10 Euro pallets, not stackable = 4.0 LDM.