Final answer:
In the ordered pair (-1,5), the number -1 represents the Abscissa, which indicates a position horizontally to the left side of the coordinate system in a 2-dimensional Cartesian coordinate system.
Step-by-step explanation:
In the ordered pair of numbers (-1,5), the number -1 is called the Abscissa. The Abscissa refers to the horizontal coordinate in a 2-dimensional Cartesian coordinate system. In such a system, the Abscissa indicates the distance along the x-axis, which can be in the positive or negative x direction of the coordinate system. Since -1 is to the left of the origin on this axis, it represents a point horizontally to the left side of the coordinate system. On the other hand, the number 5 in this pair, called the Ordinate, indicates the vertical position along the y-axis, which in this case, is vertically upward in the coordinate system.