A lot of definitions can be found in the web. More deeper information can be found In Wikipedia

Simple we can say that pivot table is a program tool that allows you to reorganize and summarize
selected columns and rows of data in a spreadsheet or database table to obtain a desired report.
A pivot table doesn't actually change the spreadsheet or database itself. In database lingo, to
pivot is to turn the data to view it from different perspectives.

jqPivotGrid is a component that you can use with jqGrid to create a pivot grid.
Let’s say that we have the following table with some sales data with the following fields:
product name, category name, country, price and quantity. If you want to edit, search delete this data,
you could easily use jqGrid features.

What would you do if you had to answer the following questions?

1. What are the order amounts of each category?
2. What are the order amounts of each in a specific country?
3. What are the order amounts and quantity of each category and product in specific country and their totals?

You could use jqPivotGrid to create those reports, and this is how they would look: