Temporary Override Keys are used to temporarily turn on or off running drafting settings: these are keyboard buttons or button combinations you can use while in a command to trigger another action. They are called temporary because they stop once you release the keyobard buttons that trigger them.
For example, while in a command holding down the Shift key toggles the current setting of Ortho mode (turn it on if it is off, turn it off if it is running). Another Example: while panning, hold SHIFT to constrain pan to horizontal and vertical movements (works in modelspace and inside viewports).
The following is a list of temporary override keys built into AutoCAD/LT by default and available to everyone:
SHIFT Toggles ORTHOMODE
SHIFT+’ Toggles OSNAP
SHIFT+, Object Snap Override: Center
SHIFT+. Toggles Polar Tracking
SHIFT+/ Toggles UCSDETECT (not in LT)
SHIFT+; Enables Object Snap Enforcement
SHIFT+] Toggles Object Snap Tracking
SHIFT+A Toggles OSNAP
SHIFT+C Object Snap Override: Center
SHIFT+D Disable All Snapping and Tracking
SHIFT+E Object Snap Override: Endpoint
SHIFT+L Disable All Snapping and Tracking
SHIFT+M Object Snap Override: Midpoint
SHIFT+P Object Snap Override: Endpoint
SHIFT+Q Toggles Object Snap Tracking
SHIFT+S Enables Object Snap Enforcement
SHIFT+V Object Snap Override: Midpoint
SHIFT+X Toggles Polar Tracking
SHIFT+Z Toggles UCSDETECT (not in LT)
You can also use the stock F-keys while in most running commands:
F3 Toggles OSNAP
F6 Toggles UCSDETECT (not in LT)
F8 Toggles ORTHOMODE
F9 Toggles SNAPMODE
F10 Toggles Polar Tracking
F11 Toggles Object Snap Tracking
F12 Toggles Dynamic Input
To create a temporary override key : explore HERE.
To modify an existing temporary override key: tap this HELP document for details.