LD stand's for high density. PE Stand's for PolyEthylene. LDPE slick's look & feel similar to HDPE slick's
The main difference being LDPE is usually thinner & softer & not as strong as HDPE. This makes the board more flexible than HDPE but mean's the board can easily crease more easily.
LDPE is usually used with EPS Core's as it is much cheaper & looks & feels very similar to HDPE slick.