Episteme
"Episteme" is a philosophical term derived from the Ancient Greek word ἐπιστήμη "epistēmē", which can refer to knowledge, science or understanding, and which comes from the verb , meaning "to know, to understand, or to be acquainted with".
Epistemic modal logic
Epistemic logic also deals with belief, not just knowledge. The basic modal operator is usually written "B" instead of "K". In this case though, the knowledge axiom no longer seems right—agents only sometimes believe the truth—so it is usually replaced with the Consistency Axiom, traditionally called D: