The Keyboard Shortcut Override Toggle lets you toggle between using only the "Main User Interface" shortcut keys and using both the main shortcuts and shortcut keys for groups such as Edit/Editable Mesh, Track View, NURBS, and so on.
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Main toolbar > (Keyboard Shortcut Override Toggle)
When the Override toggle is off, only the Main User Interface shortcuts are recognized. When Override is on, both Main UI and functional area shortcuts are recognized; however, if there is a conflict between a shortcut assigned to a feature and one assigned to the Main UI, when Override is on, the feature's shortcut takes precedence.
You can customize keyboard shortcuts on the Keyboard panel of the Customize User Interface dialog. The lists in the keyboard panel show which shortcuts have been assigned to which command or feature.