Define universal indicator and for what purpose it is used?

Hint: The common indicator cannot give us the strength of acid and base. To measure the strength of acid and bases we need a universal indicator.

Complete step by step solution:
Chemical indicator is a substance that gives a sign usually by a colour change, or the presence/ absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution.
There are many types of indicator such as Universal indicator, litmus, phenolphthalein, methyl orange, and bromothymol blue.
A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth colour changes over a wide range of pH values to indicate the acidity or alkalinity of the solution.
They are used to indicate the acidity and alkalinity of the solution by colour change.
In an acidic medium the indicator will show colors like red, orange, yellow, orangish yellow etc.
In basic medium the indicator will change its colour to blue violet or purple.
In neutral medium it will change its colour to green
Using a pH scale we can determine the strength of a solution.

Note: There is chances of confusion between universal indicator paper and litmus paper. So, for this purpose always remember that universal indicator paper shows whether die material is acid or alkaline or neutral and provides us the exact pH of the solution(generally there is a scale to look at) but litmus paper is used to test material solely acidity.