Prior to 01 Jan 2004, The New York Times will add sales of electronic books to its regular listings of "best-sellers".
How they incorporate this different medium (e.g. categories such as hardcover, paperback, electronic) is irrelevant to this claim, as long as electronic sales to consumers are considered in its best-seller list in some quantitative fashion. The list may be compiled by another source, as long as the NY Times publishes this list of electronic sales regularly with other media best-sellers on its web-site and/or newspaper.
Electronic books are those that are distributed to the consumer via electronic means. Examples include text or html downloads, pdf downloads, files on diskette.
If the NY Times ceases to exist or ceases to publish best seller lists, another well-known publication source of best-seller tracking will be selected by the judge (Los Angeles Times, Washington Post, etc.).