What is Matter Of Fact?

Legal Definition
A matter of fact, in the Humean sense, is the type of knowledge that can be characterized as arising out of one's interaction with and experience in the external world (as compared to a Relation of Ideas). In a Kantian framework, it is equivalent to the synthetic a posteriori.

Examples:
-The sun will come out tomorrow. (Not reason but habitual)
-There are people outside the room. (One cannot know what is outside one's own experience)

How We Know:
-It is impossible to "know."
-Depend upon The Principles of Induction and The Uniformity of Nature.
-Denying these do not lead to a contradiction.
-- Wikipedia
Legal Definition
Pleading. Matter which goes in denial of a declaration, and Dot in avoidance of it. Bac. Ab. Pleas, &c. G 3; Hob. 127.
-- Bouviers Law Dictionary
Legal Definition
That which is to be ascertained by the senses, or by the testimony of witnesses describing what they have perceived. Distinguished from matter of law.
-- Black's Law Dictionary
Legal Definition
An assertion or allegation of a fact's truth as this inquiry's basis.