vishNu sahasranAmam - the thousand 'names' of vishNu is part of mahAbhArata, set at the end of the great war.
In the preface of the SlOka, BhIshma, who narrates the SlOka, indicates that they represent the characteristics or qualities of vishNu. Thus the names represent the qualities and not literal names.
This section attempts to provide a visual guide to the names for easy understanding and memorization. You can also find the names and simple meanings separately in the linked page.