Value.
A function f:A->B is defined in A and takes values in B. Thus, for aA (a in A), f takes on the value of f(a)B.

Variable
A symbol, usually a small case letter, used to represent one or more numbers. e.g. In the expression 2x + 3, the variable is x. The 3 is called a constant because its value never changes.

Vertex (plural: vertices)

The point of intersection of two rays that form an angle, two sides of a polygon or two edges of a solid.

vertically opposite angles

Two angles formed by the intersection of two lines. They share a common vertex but no sides or interior points. e.g.

Vertically opposite angles, < a < c and < b < d, are congruent

Whole number.

Numbers ..., -3, -2, -1, 0, 1, 2, 3, ... are said to be integers, numbers 0, 1, 2, 3, 4, ... are called whole numbers, numbers 1, 2, 3, ... are the counting numbers.