The currency of a piece of information has to do with the time the piece of information was written. It can tell you how recent or backdated a published piece of information is.
In modern research processes, information is collated and evaluated based on the timeline in which it was written. A piece of information may have been true and valid twenty years ago, but as at our present day, it may be false.
Take for example: the information in a publication which says that Barack Obama is the current president of America may have been valid six years ago. However, the information is no longer true as the president has been changed. This makes the piece of information no longer "current"