In chemistry, pH () (potential of hydrogen) is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the molar concentration, measured in units of moles per liter, of hydrogen ions. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Pure water is neutral, at pH 7 (25°C), being neither an acid nor a base. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively. 

pH measurements are important in agronomy, medicine, biology, chemistry, agriculture, forestry, food science, environmental science, oceanography, civil engineering, chemical engineering, nutrition, water treatment and water purification, as well as many other applications. 

The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or an indicator.
what does pH mean?
what kind of scale?
what does it specify?
what is it the negative of?
measured in  what?
what are pH less than 7?
and more than 7?
what is water?
what degree?
Is it a water or a base?
Can pH be less than 10?
less than 0?
greater than 14?
What is used to measure the pH of aqueous solutions?
and what else?
potential of hydrogen
potential of hydrogen
numeric
numeric
the acidity or basicity of an aqueous solution
the acidity or basicity of an aqueous solution
the base 10 logarithm
the base 10 logarithm
moles per liter
moles per liter
acidic
acidic
basic
basic
neutral, at pH 7
neutral, at pH 7
25°C
25°C
neither
neither
Yes
pH value can be less than 0 
Yes
he pH value can be less than 0
Yes
greater than 14 
pH meter
 pH meter
a glass electrode
a glass electrode