The International Organization for Standardization, (ISO) is a worldwide organization that develops many different kinds of Standards.
ISO 9000 is a series of documents that define requirements for the Quality Management System Standard. ISO 9001 is one of the documents in this set; it contains the actual requirements an organization must be in compliance with to become ISO 9001 Registered.
ISO 9001:2008 is the current version of the Standard. It was called ISO 9001:2000 until it was revised in the year 2008,. Past versions of ISO 9000 included ISO 9002 and ISO 9003, but those are no longer in use. Companies are now only Registered to ISO 9001.