The pH of a substance depends on the relative amount of hydrogen ions in it. When we measure the pH of a substance, we are measuring how acidic or how basic it is. Think of the pH scale as a ruler - only the pH scale runs from 0 to 14.
Pure water is neutral.
Pure water has a pH of 7. Everything with pH below 7 is an acid. The strongest acids have pH from 0 to 2. Everything with pH above 7 is a base. The strongest bases have pH from 12 to 14.