if you look at my diagram and pay close attention to the color coded tail and nose, youll notice that on the lip slide, your back foot always goes over the rail, where as a board slide, your front foot goes over the rail. Basically theyre both board slides, but with exact opposite rotations to get on the rail.
A blunt slide is just like a board slide except you go over the rail a bit more to get your back foot on the rail instead of the middle of the board.
Now, to confuse you more:
A NOSE BLUNT is the exact same as a LIP SLIDE except you go over the rail a bit more to get your FRONT FOOT on the rail.
So in conclusion:
Lip Slide: Your back foot goes over the rail
Board Slide: Your front foot goes over the rail
Blunt Slide: Board slide but you slide on your back foot instead of in the middle
Nose Blunt: Lip slide but you slide on your front foot instead of in the middle