Definition and type definition
The Quick Definition popup shows you where and how a project symbol (class, method/function, field, etc) is defined:
View definition of a symbol at caret
Place the caret at a symbol in the editor and press Ctrl+Shift+I (or clickin the main menu).
Alternatively, with the Ctrl key pressed, hover the cursor over any symbol. CLion displays the symbol as a link and shows its definition in a tooltip. Click this link to jump to the definition of the symbol.
You can open a definition in the Find tool window. To do so, click the icon in the top-right corner of the popup and click Open in Find Tool Window.
To open the source code of the definition for editing and close the popup, click the icon and then click Edit Source (F4).