Tacit knowledge is a process of knowing something but not being able to explain it.  Tacit knowledge is locked inside of our heads, and it is hard to articulate it.  This kind of thinking or knowing is ingrained in us by our culture, our personal habits, and our experiences as we grow up.  Tacit knowledge is not easily shared with another person, unless there is a great deal of trust.  For instance, if you learn to ride a bicycle, it is not a process that you get from a book, it is an experiment that you continue to try until you either fail, or succeed at it.  Some theorists feel that tacit knowledge is how we approach innovative thinking and create something new from the idea of a need for something unknown.  Explicit knowledge is what we get from  fact finding, reading manuals and documents, and studying procedures.  This kind of knowledge can be easily shared.