Save Filter is a tool that will allow you to save a certain set of filters which are applied often in a document list or a report so that you can reuse them.
To learn more about filters, checkout Search Filter
Let's say, in purchase orders, you need to search for all the purchase orders where the Grand Total is more than ₹ 10000. However, as we know, there is no filter that is present for it out of the box.
In this case, you can create a custom filter for it and save the same condition in the 'Save Filter' option for you to easily access this filter every time you open the Purchase Order list.
To save a Custom Filter, you may go to the 'Save Filter' option in the Left Sidebar of the list or the report.