This legal concept, which originated in U.S. law, permits certain uses of copyrighted works that are prohibited per se if they qualify as – literally – fair or equitable use. post 
In order to determine whether a certain use is "fair," the following factors in particular are taken into account in addition to the nature of the work (for the whole, see for instance Helms, S. & Krieser, J. (March 2023). Copyright Chaos: Legal Implications of Generative AI. Bloomberg Law page ): [...]
~
OEHRI, Isabelle, 2023. Chat GPT & Co. - Was sagt das Urheberrecht? Management and Law Blog [online]. 5 April 2023. [Zugriff am: 14 April 2023]. Verfügbar unter: https://hub.hslu.ch/management-and-law/2023/04/05/chat-gpt-co-was-sagt-das-urheberrecht/