An OBI Strip is a piece of paper wrapped around the spine of Japanese CDs, DVDs, Movies, or Books sometimes referred to as a "Spine Card".
They started in Japan as a way of providing Kanji translations to overseas CDs imported into Japan, but have since become a standard part of a new CD providing Label, CatalogCode, UniversalProductCode, and other information that usually clutters the back of a CD. Most people simply discard and ignore them after unwrapping the plastic from a CD since the info contained on them are mainly for the seller and not the buyer. But to the collector market they’re a rare commodity that can increase the collector price of the CD; and in the case of MusicBrainz they provide a wealth of information that isn’t reproduced on the Album itself and often more info that most western CDs contain (such as price and original release date).
Standard on all OBI's is the barcode. It's not reproduced on the album so an album missing a barcode isn't necessarily a bootleg or pirated CD in Japan.
Label name and Catalog Number are also on the OBI.
The price is usually listed both with tax and without.
A few dates are usually on the OBI, one is the official release date that the CD first hit stores, the other is the date that the retailer is allowed to start selling at a price different from what is listed on the OBI. Occasionally for re-masters and re-releases the date of the albums first release will be listed. This is common when an old vinyl album is first released on CD.
Track listings are usually listed especially if they aren’t on the back of the album or if the album is imported the track listing on the OBI will be the transliteration to Kanji or Kana. It will also usually point out any special/bonus/hidden tracks that don’t show on the back of album.
Enhanced disc features and requirements are ofted written on the OBI.
Any extra space left on this thin piece of paper is usually given to advertising upcoming tour dates, or albums from the rest of the artist’s discography.
For local Japanese releases the OBI strip has become an integral part of the packaging and not just a place to put transliterated info. In true modern Japanese form the OBI is information overload with flashy text; the background of the OBI strip is colored to blend with the cover as it overlaps the black or clear CD tray on the left of the cover to create seamless art from front to back. And even when the CD case is packaged in a cardboard sleeve the case inside often still has an OBI wrapped around it with additional information.