pH is used to define how acidic a solution is. Scientist use a pH scale ranging from 0 to 14 to represent pH. This is a relative measure of the hydrogen ion concentration in a solution. The less Hydrogen ions in a solution the more basic (alkaline) it is, the more Hydrogen ions in a solution then the more acidic the solution is. On a pH scale anything below 7 is acidic, solutions at 7 are neutral and anything above 7 are basic. Other ways you can verify the pH of a solution include using pH indicator papers as well as pH meters.
Below is a video explaining more about pH.
Below is a video explaining more about pH.