Instead of searching an entire database (like a .DBF file) from start to finish, the program looks at the .IDX file to find the exact location of the data.

The file extension is a generic extension used by several different programs, but its core purpose is almost always the same: to index data for faster searching or access.

.idx files can also be used in other contexts, such as:

Many database systems or specific applications create .idx files to speed up searches.