Bianca put a layer of packing tape around the top outside edges of a box to ship it.
The measurement that represents the total amount of packing tape that she used is - the perimeter of the top of the box
Perimeter is defined as the measurement of the outer lines or edges of any figure. As there is a box and only the outer edges are covered with tape, it means that Bianca has used the tape equaling the total perimeter of the top.
It can be more clear with this example
Suppose the box is rectangular with top dimensions 10 inches and 5 inches.
So, perimeter is length+width+length+width
or 2(length+width)
perimeter = 2(10+5) = 30 units. So, Bianca used 30 units of tape.