Solid block

Solid blocks consist of any type of block that has a collision box that players, mobs, or other entities cannot simply move through, and have to move on top of it or around it. Solid blocks are significantly different from liquid or gas blocks, through which entities can freely pass.

Mobs require a solid top surface to spawn. Some mobs are able to spawn inside of the space occupied by another block, but only if their hitbox does not intersect the collision of any solid block.

Players, mobs, and other entities can walk on top of solid blocks. Particles that are affected by gravity (e.g. slime particles or water drip particles) also collide with solid blocks.