# Glossary

Short definitions of Swarm-specific terms used throughout this book.
Each entry links to the chapter where the concept is developed in
full.

### BMT (Binary Merkle Tree)
The hash construction Swarm uses to address chunks. Operates on
4 KiB blocks with keccak256 as the underlying hash. Produces a
32-byte address per chunk. The structural alternative to a flat
sha-256 hash.

### Batch (postage batch)
A pre-funded allowance of chunk-storage capacity bought on-chain.
Identified by a 32-byte ID. Every chunk uploaded to Swarm needs to
be stamped with a batch; when the batch expires, storer nodes
eventually drop the chunks. See
[Postage batches and re-seeding](./concepts/postage.md).

### Chunk
The unit of storage in Swarm — up to 4 KiB of bytes, addressed by
its BMT hash. Everything in Swarm (files, manifests, feed updates)
is ultimately a graph of chunks.

### Deferred upload
Bee's default upload mode: the API accepts your data, returns the
reference immediately, and pushes the chunks into the network in
the background. Fast but means there's a window where the reference
exists locally and isn't yet retrievable network-wide. See
["My upload looks lost"](./cookbook/lost-upload.md).

### Feed
Swarm's mutable-name primitive — the analog of IPNS / DNSLink.
Identified by an `(owner, topic)` pair where owner is a 20-byte
Ethereum address and topic is a 32-byte hash. Resolved via
`GET /feeds/{owner}/{topic}`. See
[Swarm references vs IPFS CIDs](./concepts/swarm-refs.md).

### Gateway (public gateway)
A public Bee node exposed over HTTPS that serves `GET /bzz/{ref}/`
without auth. `bee-check --gateway <URL>` HEAD-probes one as an
external retrievability vantage. Default is
`https://api.gateway.ethswarm.org`.

### Manifest
A Mantaray-encoded trie stored as a graph of chunks. Maps paths
(like file paths) to chunk references. What `GET /bzz/{ref}/path`
walks. See
[Manifests and per-chunk drill-down](./concepts/manifests.md).

### Mantaray
The serialization format used for manifests. Each node fits in one
chunk and has up to 256 forks (one per first-byte of a child path).
Nodes can also carry a `target_address` pointing at content chunks.

### Neighborhood
The first byte of an overlay or chunk address, by convention used
to describe "where in the address space" something lives. A chunk
in neighborhood `0x4a` is one whose address starts `0x4a…`; storer
nodes with overlays starting `0x4a…` are the chunk's primary
neighbors. See [Proximity](./concepts/proximity.md).

### Overlay (overlay address)
A node's 32-byte identifier in the same address space as chunk
references. Determines which chunks the node is responsible for.
`GET /addresses` returns it. `bee-check` surfaces each vantage's
overlay so you can read its neighborhood.

### PO (proximity order)
The number of leading bits two 32-byte values share. PO 0 = no
shared bits; PO 8 = same first byte (same neighborhood); PO 256 =
identical. The closeness metric in Swarm's address space. See
[Proximity](./concepts/proximity.md).

### Reference
A 32-byte (64-hex) or 64-byte (128-hex, encrypted) Swarm address.
Can point at a raw chunk, a manifest root, or a feed update. The
input `bee-check` takes.

### Re-seed
Re-uploading a reference's chunks under a fresh postage batch,
typically to refresh stamps before a batch expires. `bee-check
--reseed --stamp <id>` does the pre-flight + `PUT /stewardship/{ref}`
flow. See [Postage and re-seeding](./concepts/postage.md).

### SOC (single-owner chunk)
A chunk whose address is `(owner_address, topic)`-derived rather
than content-derived. The substrate underneath feeds — each feed
update is a SOC. Not directly addressed by `bee-check` today.

### Stamp
The cryptographic proof that a chunk's storage is paid for by a
specific postage batch. Storer nodes only keep chunks with valid
stamps; expired-batch chunks are eventually garbage-collected.

### Stewardship probe
The `GET /stewardship/{ref}` endpoint a Bee node exposes. Walks
the manifest at `ref` and tries to fetch every chunk *through the
network retrieval path*, returning `{ "isRetrievable": true|false }`.
Different from `/bzz` which serves from local store when possible.
See [The stewardship probe](./concepts/stewardship.md).

### Vantage
In `bee-check`, one `--bee` URL — a single perspective on
retrievability. Multi-vantage probing samples retrievability from
multiple points in the network. See
[Multi-vantage](./concepts/multi-vantage.md).
