From [[ https://en.wikipedia.org/wiki/Web_of_trust | Web of Trust (wikipedia) ]]
> In cryptography, a web of trust is a concept used in PGP, GnuPG, and other OpenPGP-compatible systems to establish the authenticity of the binding between a public key and its owner. Its decentralized trust model is an alternative to the centralized trust model of a public key infrastructure (PKI), which relies exclusively on a certificate authority (or a hierarchy of such). As with computer networks, there are many independent webs of trust, and any user (through their identity certificate) can be a part of, and a link between, multiple webs.
From [[ https://tails.boum.org/install/download/index.en.html | Tails: Verify using OpenPGP ]]
> Verifying using OpenPGP but without authenticating our signing key through the OpenPGP Web of Trust is equivalent in terms of security to verifying using our browser extension or BitTorrent because it relies on downloading a genuine signing key from our website.