To format data in such a way that it can be used by another application. An application that can export data can create a file in a format that another application understands, enabling the two programs to share the same data. The two programs might be different types of word processors, or one could be a word processor while the other could be a database management system.
The flip side of exporting is importing. Importing refers to the ability of an application to read and use data produced by a different application. Exporting implies that the sending application reformats the data for the receiving application, whereas importing implies that the receiving application does the reformatting.