From Science Europe Data Glossary
Definition: digital preservation is a formal endeavor to ensure that digital information of continuing value remains accessible and usable.
Explanation: digital preservation involves planning, resource allocation, and application of preservation methods and technologies, and it combines policies, strategies and actions to ensure access to reformatted and "born-digital" content, regardless of the challenges of media failure and technological change. The goal of digital preservation is the accurate rendering of authenticated content over time.
Alternative definition: according to Harrod's Librarian Glossary, digital preservation is the method of keeping digital material alive so that they remain usable as technological advances render original hardware and software specification obsolete.
References: http://en.wikipedia.org/wiki/Digital_preservation; Raymond John Prytherch, Harrod's librarians' glossary and reference book : a directory of over 10,200 terms, organizations, projects and acronyms in the areas of information management, library science, publishing and archive management, (Aldershot, Hants, England ; Burlington, VT : Ashgate, 2005), see: http://www.worldcat.org/title/harrods-librarians-glossary-and-reference-book-a-directory-of-over-10200-terms-organizations-projects-and-acronyms-in-the-areas-of-information-management-library-science-publishing-and-archive-management/oclc/498499718
See also: data archiving