Terminology

Anchor - Large (over 100K) file from package. Anchors are used to fetch HashPackages from HashServer.

DirHashDB - Local HashDB stored in filesystem directory.

HashDB - Collection of HashPackages, local (DirHashDB) or remote (HashServer)

HashPackage - Small local representation of package, which has URL of remote package and list of file hashes which could be extracted from that package

HashServer - remote HashDB with HTTP interface

Package - Remote file (most often - archive) which can contain one or more file. For example, linux kernel archive, wordpress archive and vim .deb package are all Packages.

Signature and Signature Type - Unique combination which identifies package. For example, for vim package:

    "signatures": {
        "url": "http://snapshot.debian.org/archive/debian/20171002T041924Z/pool/main/v/vim/vim-common_8.0.0197-4+deb9u1_all.deb",
        "deb": "vim-common_8.0.0197-4+deb9u1_all"
    },