Definition - What does Safe Mode mean?
Safe mode is a boot option in which the operating system starts in diagnostic mode rather than in normal operating mode. It is used primarily for troubleshooting a system that has crashed, failed to boot correctly or is experiencing instability after installing an update, device driver or new software installation.
Safe mode is also known as safe boot.
Techopedia explains Safe Mode
Safe mode is intended primarily for maintenance or troubleshooting. In this mode, the operating system loads only a minimal set of drivers and services to allow the isolation of problems causing system instability. Utilities and diagnostic programs are available during this state. Networking may or may not be available, depending on the settings used. Audio is often disabled, whereas the video uses a low resolution since the drivers for these devices are among those not loaded by default.
Users may explicitly select to boot in safe mode or the operating system may default to it or suggest it at boot time, especially after a prior crash.