A pH of 7 is known as a neutral pH in chemistry. Pure water is a neutral compound. As substances approach a pH of 0, they become more acidic, and as they approach a pH of 14, they become more basic.
A pH level represents the concentration of hydrogen ions in water. A substance that is acidic with a lower pH level has a higher concentration of hydrogen ions than a substance that is basic with a higher pH. There is also a pOH scale that represents the concentration of hydroxyl ions. It goes from 0 to 14 just like the pH scale, but below 7 is basic and above 7 is acidic with 7 being neutral.