Windows shortcut
CtrlF3
Mac shortcut
Fn⌃F3
In Windows, this shortcut now displays the Name Manager dialog, where you can click the New button, to create a new name. There is no actual shortcut for to create a single new name, except through the ribbon: Alt M + MD
On a Mac, this shortcut displays the Define Name dialog box, which offers to name a range based on the current selection.