Explicit knowledge is characterized by the fact that it can be captured in some form: it can be a book, a course, a seminar, or any other medium. It is the most basic form of knowledge, and the one we usually think about when we imagining expertise.
For example, if I’m studying a new programming language, the syntax rules of the language can always be found in a manual.
This is in contrast with tacit knowledge, which cannot be captured.