Grass Slabs were introduced with Patch R36 on November 15th 2016.
2 of these slabs can be made in a Processor from one block of green Grass each. No crafting recipe has to be unlocked for that.
Grass is a very common surface block that can be found in many Biomes, such like Grassland, Woodlands, Forests and Swamplands.
Obtaining Grass Slabs is the one requirement necessary to unlock the crafting recipe for Grass Stairs. Grass Slabs are also the one ingredient required to craft Grass Stairs.
Different from cubic blocks ordinary green Grass, Grass Slabs cannot be corrupted by Corrupt Bombs nor by Corrupted Water.
Grass Slabs will not turn blocks of Dirt next to them into blocks of Grass.
Dead Grass and Savannah Grass cannot be processed into Grass Slabs.