Define normal
From reference.com (and I quote)
nor·mal   [nawr-muhl] Show IPA
adjective
1.
conforming to the standard or the common type; usual; not abnormal; regular; natural.
2.
serving to establish a standard.
3.
Psychology .
a.approximately average in any psychological trait, as intelligence, personality, or emotional adjustment.
b.free from any mental disorder; sane.
4.
Biology, Medicine/Medical .
a. free from any infection or other form of disease or malformation, or from experimental therapy or manipulation.
b. of natural occurrence.
5.
Mathematics .
a.being at right angles, as a line; perpendicular.
b. of the nature of or pertaining to a mathematical normal.
c. (of an orthogonal system of real functions) defined so that the integral of the square of the absolute value of any function is 1.
d. (of a topological space) having the property that corresponding to every pair of disjoint closed sets are two disjoint open sets, each containing one of the closed sets.
e. (of a subgroup) having the property that the same set of elements results when all the elements of the subgroup are operated on consistently on the left and consistently on the right by any element of the group; invariant.
