The index is used to search the data in a table.
The index is basically a data structure that search our data.
It is applied usually on a column of a table.
It is usually a B-tree but can also be hash table and other depending upon the need.
It is usually applied on a primary key column.
If we want to search the detail of a person named Ishan and if we do not apply the index it has to search for Ishan the whole table.
If we apply indexing then it will just look into the index which will give the index number of the Ishan and then the detail of the corresponding will be displayed.