Macrium refers to Macrium Reflect, a disk imaging, backup and recovery solution for Windows. Questions involving the use of this product should use this tag; you might also like to consider using [tag:images], [tag:backup], [tag:recovery], [tag:windows-backup].

What is it?
Macrium Reflect is a disk imaging solution for Windows, capable of taking a full image of a disk for recovery at a later point in time. Macrium can create full, differential or incremental disk images and uses the Windows Volume Shadow copy service for maximum compatibility across Windows versions.
What does it support?
Macrium Reflect supports windows-xp, windows-vista, windows-7 in 32 and 64-bit varieties. It supports mbr-based disks as well as gpt disks, uefi boot etc. It is capable of backing up, from Windows, ntfs, fat32 and ext4 based volumes.
For restoring, reflect supports a windows-pe based recovery environment, as well as a linux based rescue CD, for restoring systems that are no longer bootable from a backed up image.
Further reading on backups, disk imaging etc: