Handover is a term which simply describes the handing over of the keys to the new owner. Because the date occurs between two other legislated dates (that is - after practical completion and before the end of the defects libility period) and also represents the owner being allowed by the builder top "take control" the home, it is commonly misunderstood that handover is the day that building work should be completed. In accordance with legislation this is not what handover means.
Handover within most building contracts is considered symbolic in that it is not the date that the final building payment is due (commonly due at practical completion - although may vary between builders), nor is it the date that the building should be ready for expected use (that date is called Practical Completion), nor does it represent the date that the building work is to be completed (defects liability period).
Note: It is worth noting that building contracts will always vary, and although contracts are required to comply with legislation the date payments are due etc.. is generally not legislated and will alter- check your contract for details of what the above definaitions mean for you.