On the scale of stuff with a pH
Did you not carry out some research?

Well, you can find information about it in Wikipedia, or even dictionaries like Merriam-Webster or Dictionary Online.

You will see that pH is calculated through:

$$pH = -\log(a_{\ce{H+}})$$

Or which can most of the time be stated as:

$$pH = -\log(\ce{[H+]})$$

$a_{\ce{H+}}$ is the hydrogen ion activity, the 'effective concentration' of hydrogen ions. Without active hydrogen ions, you don't have any pH.

You might find that the pH scale is from 0 to 14, but you can also have circumstances where you have negative pH and pH above 14. It depends on the extent of dissociation of an acid or base to produce active hydrogen ions, or hydroxide ions in the case of bases.

Since I mentioned hydroxide ions, it might also be worth nothing that:

$$14 = pH + pOH$$

And that basically, a pH of 1 is equivalent to a pOH of 13.