xD-Picture Card is the proper form of the title. And not XD- this is due to a known limitation of the MediaWiki software used on this site.
Like Sony's Memory Stick, xD was not as successful as hoped and fell technically behind Secure Digital. For this reason, Fuji began double xD / Secure Digital slots in their compact cameras from the FinePix F40fd onward. Olympus has proved more resistant to dropping the xD format, instead adding software rather than physical compatibility for SD, allowing smaller form factor SD cards to be used via an adaptor.