OK, I'll try and explain.
Backup - copying files to tape or a disk so that you can recover a system if the files get corrupt.
Image backup - Full copy of a disk on a Computer
Incremental Backup - Copy of all files that were changed since the last Image Backup
Operating System - On your PC it could be XP or Vista. Servers might be VMS or Unix.
Server - A Computer in a remote site from your PC.
Mirrored Servers - 2 Servers both sharing the work, doing half each. If one fails, then the other takes the full workload until the other is fixed.
Offsite Backup - Keeping a copy of the files on a Server in a location away from the building the Server is in. Therefore if the Building the Server is in burns down, then you can recover all the files easily and get the system up and running quickly on a new Server.
Virtual system - A big Computer that is segregated into doing several applications at once (HMVF being just one), so that it appears to be several Computers rather than just one.
Most of my working life was running Housekeeping routines on Computer systems, mainly ICL, Burroughs and Dec VAX.