What is the meaning of Simplex?

Single, simple; not complex.

Unidirectional.

An analogue in a space of arbitrary dimensionality of the triangle or tetrahedron; the convex hull of n+1 linearly independent points in n-dimensional space; in other words, the triangle, tetrahedron etc., generalized to an arbitrary number of dimensions.

A monomorphemic word, one that is not compound and contains no derivational affixes

single

simple, plain, uncompounded

pure, unmixed

sincere, naive, frank, open, without guile, guileless, unsuspecting, innocent

simplex

Source: wiktionary.org