Blocks are a type of item in Minecraft. They make up the in-game environment, and can be collected and utilized in different ways. Some blocks are created naturally, such as dirt or stone, while others, such as Bricks or Redstone Lamps, must be crafted by the player.
Certain blocks have special uses, such as Jack-O-Lanterns, Glowstone and Redstone Lamps which can be used to light underwater areas, as they cannot be put out by water (if the Redstone signal going to the redstone lamp is not destroyed).
There are three different transparency levels of blocks. There are completely transparent blocks like air. There are semi-transparent blocks like glass and leaves. There are also blocks with 0% transparency, like wood or cobblestone. Most blocks that are at least some what transparent will not be able to have torches placed on them.
The face of a block is 16×16 pixels, and each block is proportionately one cubic meter. Most blocks are static, although Water, Lava, Portal, and Fire blocks have a shifting pattern for each side. While the default texture pack's textures are 16x16, there are texture packs with 32x32 or even 64x64 textures. These texture packs often require a mod.