Knowledge is certain conviction that matches reality. Such that if one is certain that some belief is true, and this belief is actually true, then this belief is also knowledge.
Types of Knowledge
Knowledge is of two kinds: conceptual (Taswiri) and propositional (Tasdiqi).
Conceptual: knowledge of a meaning. For example: knowledge of what “God” means. This known meaning is called a concept.
Propositional: knowledge of a relation between two concepts. For example: knowledge that “God exists”, where “existence” is related to “God”. The statement “God exists” is called a proposition.
Complexity of Knowledge
Each of conceptual and propositional knowledge is further divided into two sub-categories depending on the complexity of the known information: the non-inferential (Daruri), and the inferential (Nazari).
Non-inferential: information that does not require pondering to be known. For example: knowledge that “1 + 1 = 2”.
Inferential: information that does require pondering to be known. For example: knowledge that “14 × 6.5 = 91”.
The complexity of some information is subjective to the thinker. Some facts may be non-inferential to some people, while being inferential to others. Some facts may even be inferential for one person at one time, and non-inferential for this same person at another time.
Non-inferentially conceptual: knowledge of a meaning that requires no pondering to be known. For example: knowledge of what “existence” means.
Inferentially conceptual: knowledge of a meaning that requires pondering to be known. For example: knowledge of what “quark” means.
Non-inferentially propositional: knowledge of a relation between two concepts, that requires no pondering to be known. For example: knowledge that “the whole of a body is larger than each of its parts”.
Inferentially propositional: knowledge of a relation between two concepts, that requires pondering to be known. For example: knowledge that “God exists”.
 By “knowledge” in this context, we mean human knowledge specifically.
 We say “some information” because some other facts are non-inferential for every Mukalaf, at all times. These fundamental facts are called “axioms” (Badihiyat). Such that all axioms are non-inferential, but not all non-inferential information is axiomatic.
For example: every Mukalaf knows that he himself exists.
The necessity of axioms is discussed here.
 In fact, the meaning of “existence” is so basic, its definition may even be ineffable. This is because one of the purposes of a definition is to explicate on what a word means by using simpler terms, and “existence” cannot be simplified any further.