Solid block is the term for a block which the player cannot walk through. This has nothing to do with whether a block can be seen through or the game treats the block as transparent (for example, glass is a solid block but can be seen through and is treated as transparent). Most block types are solid, while most plant types are not. Cacti, wood, pumpkins and leaves are all examples of solid plant blocks. Ladders may not seem solid, but it is possible to stand atop them without descending.
Both water and lava are not solid, and can be passed through (although passing through lava will deal damage to the player, so this is strongly not recommended.). Every type of solid block, with the exception of bedrock can be destroyed and collected.
The only exception is Soul Sand (found in the Nether) in that when you step on to it your speed is slowed and you'll sink slightly into it, making it a half solid block. Soul Sand has other characteristics different to normal blocks such as when it's placed on top of ice or in water its slowing effects are strengthened. It is also 7/8 the height of a normal solid block. These characteristics make it an abnormal solid block.
Heights
Most solid blocks are 1 Square Meter high, but certain blocks have non-standard block heights, some of which allow the player to automatically move onto them without jumping on the surface. This is apparent with soul sand, as it can be used in front of a 1 x 2 block doorway to create a one-way entrance. This is due to the fact that soul sand is slightly less than 1 block in height.
Here is a list of blocks with non-standard heights, from tallest to shortest in height:
| Height (decimal) | Height (fractional) | Block types |
|---|---|---|
| 2.0 | 2 | Door |
| 1.5 | 1 1/2 | Fence, Cobblestone Wall [remark 1] |
| 0.875 | 7/8 | Soul Sand, Chest, Brewing Stand (stand part) |
| 0.8125 | 13/16 | End Portal Frame (without Eye of Ender) |
| 0.75 | 3/4 | Enchantment Table, Cocoa Bean (plant), Head (on wall) |
| 0.5625 | 9/16 | Bed |
| 0.5 | 1/2 | Slab, Head (on ground), bottom part of stair |
| 0.4375 | 7/16 | Cake |
| 0.375 | 3/8 | Daylight Sensor, Flower Pot |
| 0.3125 | 5/16 | Inside of cauldron |
| 0.125 | 1/8 | Brewing Stand (base), Redstone Repeater, Trapdoor, Snow [remark 2] |
| 0.015625 | 1/64 | Lily Pad |