Overview#Link Relation Types is defined in RFC 5988 as an IANA Registry which can be found at: https://www.iana.org/assignments/link-relations/link-relations.xhtml#link-relations-1
Links and operations are consumed by machines who understand their meaning because they are standardized. These names are usually defined in human readable documentation, such as the one accompanying the API, the IANA Link Relation Registry or schema.org.
As the usage of schema.org increases through it being the agreed upon vocabulary for the Structured Data initiatives of Google, Microsoft, Yahoo and Yandex for their search engines, its usage is surely going to increase for APIs as well. With a few standardized vocabularies and a few standardized hypermedia formats supporting them (such as Hydra), clients can stop being unique snowflakes coupled to specific APIs and instead move in the direction of generality and re-usability.