A slime block is a sticky building block: when pushed by a piston it drags most adjacent blocks along with it, which is what makes multi-block flying machines possible.
Bedrock Edition · Block dictionary
Slime Block — spec
Sticks to
Most adjacent blocks
Does not stick to
Obsidian, glazed terracotta, honey
Conducts
Carries strong power
Use
Binds blocks into a moving group for flying machines
