Evergreen is a Digital garden concept, used to mark articles that are published publicly as being complete with an expected long-term life of relevancy. Articles can begin as seedlings, Budding, or even in their final status dependent on how much development work is done in private vs public.
The term is also used in marketing to categorise articles which are expected to, or have, relevance over the long term.
See The value of growth maturity in a digital garden is marginal for a discussion of why notes are not marked Evergreen in this Digital garden.