The term has a long history - as the Wikipedia page [0] points out, "knowledge base" was used to distinguish systems that could actively reason about data using rules (and a rules-engine to run them) -- e.g. expert systems -- from databases, where the data just sits there. However, these days, it's used differently:
From the Wikipedia page[0]:
Knowledge management products adopted the term "knowledge-base" to describe their repositories but the meaning had a subtle difference. In the case of previous knowledge-based systems the knowledge was primarily for the use of an automated system, to reason about and draw conclusions about the world. With knowledge management products the knowledge was primarily meant for humans, for example to serve as a repository of manuals, procedures, policies, best practices, reusable designs and code, etc. Of course in both cases the distinctions between the uses and kinds of systems were ill defined. As the technology scaled up it was rare to find a system that could really be cleanly classified as knowledge-based in the sense of an expert system that performed automated reasoning and knowledge-based in the sense of knowledge management that provided knowledge in the form of documents and media that could be leveraged by humans
From the Wikipedia page[0]:
Knowledge management products adopted the term "knowledge-base" to describe their repositories but the meaning had a subtle difference. In the case of previous knowledge-based systems the knowledge was primarily for the use of an automated system, to reason about and draw conclusions about the world. With knowledge management products the knowledge was primarily meant for humans, for example to serve as a repository of manuals, procedures, policies, best practices, reusable designs and code, etc. Of course in both cases the distinctions between the uses and kinds of systems were ill defined. As the technology scaled up it was rare to find a system that could really be cleanly classified as knowledge-based in the sense of an expert system that performed automated reasoning and knowledge-based in the sense of knowledge management that provided knowledge in the form of documents and media that could be leveraged by humans
[0] https://en.wikipedia.org/wiki/Knowledge_base