The term GitOps was presented in 2018 by Weaveworks company. Briefly, it's the approach to perform the operations in the same way as developer teams usually do when working with git. When we are talking about general git flow - for any application code, you have git repository, where you define your application and git serves as a single source of truth (ideally, but it is not the case sometimes, almost everyone had experience where changes were applied directly in production to quickly fix something).
So the similar git flow approach is being applied to any Operations, git serves as a single source of truth. And only the CD instrument, that is connected to it, has ability and permissions to update the configuration and/or infrastructure.
Long story in a few words - with emerging of more and more tools that natively allow gitops (JenkinsX, ArgoCD, Tekton, Spinnaker, Flux) - more companies see the benefit to start using this in their day-to-day work.