Recovery volume

A recovery volume, previously recovery partition, is a hidden section of a macOS or Mac OS X startup drive which contains software for macOS Recovery in case a user's installation of macOS or Mac OS X becomes corrupted or unbootable.

Contents
Stored as "Recovery HD", the contents are comparable to that of an installation DVD-ROM. If the recovery volume itself is damaged, the Mac will switch to Internet Recovery and download the software from an Apple server.

The following utilities are included:


 * Restore from Time Machine backup.
 * Reinstall macOS (by default the version that shipped with the computer).
 * Safari, a basic installation for browsing Apple Support.
 * Disk Utility, to repair or erase a corrupted drive.

History
Mac Recovery Mode was first introduced in 2011 with Mac OS X 10.7 (Lion) and was stored in a hidden HFS Plus partition. Starting with the introduction of APFS in macOS High Sierra (10.13) in 2017, the "Recovery HD" was stored in a hidden volume instead of a partition.