The Fediseer is a service for the Fediverse which attempts to provide a crowd-sourced human-curated spam/ham classification of Fediverse instances as well as provide a public space to specify approval/disapproval of other instances. Here you can find the blog post announcing Fediseer.
In simple terms, using the Fediseer, we attempt to figure out whether an instance is spam or not, through a human-driven system called the “chain of trust”.
The three main concepts used in Fediseer are guarantees, endorsements and censures.
The Fediseer provides a machine readable API to consume the data contained within.
Glossary and GUI front end: https://gui.fediseer.com/glossary