All pages in HASH, including both documents and canvases, are made up of blocks.
You can read more about blocks in the HASH User Guide to learn more about what they are, how they can be used, and to see examples.
Blocks are one of the most exciting ways in which HASH can be customized, extended, and made more useful. All blocks in HASH are based on the open-source Block Protocol, a free standard for developing blocks that work in any application which supports the protocol.
At present, this includes both HASH (fully-supported) and WordPress (experimentally, via a plugin). As a result, anybody who knows how to code can develop blocks which are usable in HASH.