pH means parts Hydrogen. It is a measure of the concentration of Hydrogen ions in the solution.
pH is the negative log of the hydrogen ion concentration.
Since pH is the negative log it means that the lower the pH the more acid the solution is
Example if the solution is 10% ( 10/100) or .1
The log is the exponent of the hydrogen ion concentration so the log is -1 but pH is the negative log so
Example if the solutions is only 1% ( 1/100) or .01
So as the pH number goes up in value the hydrogen ion concentration goes down, and the solution becomes less acidic.