The pH is a measure of the acidity or alkalinity of a solution and is defined as the logarithm of the reciprocal concentration of the hydrogen ions (mol/dm³) of the solution
pH can have values from 0 to 14.
Pure water is considered to be neutral, its pH is equal to 7, and this value is used as starting point to classify solutions with respect to their pH.
A solution with a pH < 7 is considered acid.
A solution with a pH = 7 is considered neutral.
A solution with a pH >7 is considered basic.
With this in mind, you can construct a pH scale.
Values of pH close to pH=7 can be considered as "weak", so, for example, values of pH between 6.9 and 5.6, you can consider the solution to be a weak acid.
An example of a weak acid is Milk, which has a pH between 6.5 and 6.7
For values of pH between 7.1 and 8.4, you can consider the solution to be a weak base.
An example of a weak base is human blood its pH is between 7.35 and 7.45
For values of pH of 5.5 or less can be considered as a strong acid, the closer the value is to zero, the stronger the acid.
An example of a strong acid is stomach acid, which has a ph between 1 and 3
For values of pH 8.5 or more, you can consider the solution to be a strong base. The closer the pH is to 14, the more alkaline will be the substance.
An example of a strong base is Bleach, which has a pH between 11 and 13