Which of the following describes the 'input' in a function?

In a function, the 'input' specifically refers to the x-values, which are the independent variables upon which the function's output (or dependent variable) depends. When a function is defined, each input value corresponds to exactly one output value. This relationship is fundamental in understanding how functions operate; for every x-value that you input into a function, you will receive a corresponding y-value as output.

To further clarify, the relationship that defines a function is generally expressed as y = f(x), where 'f' denotes the function. The x-values represent the input to this function, driving the computation that yields the output (the y-values). Thus, identifying the x-values as the input aligns perfectly with the definition of a function in mathematics.

The other options derive from different aspects of a function and are not correct descriptions of 'input.' For example, y-values represent the outcome rather than the input. The set of coordinates includes both x and y values, which makes it less precise in describing just the input. The difference between the highest and lowest values pertains to a measure of range or spread within a dataset, which does not define input in the context of functions.