The term "conservation" refers to the protection, or stabilisation, of artefacts, sites or monuments. Conservation means protecting the past for future generations; it may involve assessment, regulating development, or remedial work where necessary.
Conservation is connected to both preservation and restoration, but the terms have quite different meanings. Preservation means preserving something in the state it is in; whereas restoration means restoring something to how it used to be. Conservation stands somewhere in between the two!
The reason for conservation, quite simply, is that the heritage is constantly at risk from various factors. Without an active policy for conservation much of our heritage would disappear within our lifetimes, and the potential it has to interest, enthuse and inform us about the past - and the future - would disappear also.