Minecraft wiki entry for Slab, associated text: Brick slabs.
Stone brick slabs.
Double smooth stone slab (left) compared to smooth stone.
Slabs used to create the impression of half-aligned full blocks.
All eight types of wooden slabs.
Trapdoors on slabs.
Example of slab shelving by placing slabs below other slabs.
Cut sandstone (left) compared to Smooth stone (right).
Slabs can carry redstone signal.