Style linking is where the Regular, Italic, Bold and Bold Italic styles (known as RIBBI) are contained within the Regular style and accessible through the (Ctrl + b / ⌘ + b) and (Ctrl + i / ⌘ + i) shortcut links. 

You may notice that in Microsoft Office applications some styles are ‘missing’ from the dropdown menu, despite appearing in other applications and being installed on your desktop. In certain Microsoft Office applications style linking can mean that the Italic, Bold and Bold Italic styles are only available through the shortcut keys. In other applications RIBBI styles will be available in both the dropdown menu and through the shortcut commands. 

Although this can be a little confusing for the end user, style linking prevents operating systems applying a “Faux Bold” and “Faux Italic” effect, where the (Ctrl + b / ⌘ + b) and (Ctrl + i / ⌘ + i) shortcut links will cause the system to apply a counterfeit Bold and Italic effect rather than connecting to the true Bold or Italic style.