Indexing is the name of the process by which computer software is able to tie related data to documents/computer files. In other words, an index lists the important data about a document.
For example, your document might be a scanned invoice. The important data for this document will be the invoice date, invoice number, PO number, etc. When we index this invoice, the end result is an orderly database of business information which can be searched and interacted with much more quickly than by physically retrieving the invoice or visually examining the scanned image.
Indexing can be done manually, but the more efficient method is to index automatically using a scanner and capture software that supports Optical Character Recognition/OCR. This method uses intelligent software algorithms in order to recognize the characters printed on the page and extracts the data into usable computer data.