Selecting
This page discusses selection tools that are specific to the 3D Viewport. The generic selection tools are described in the Interface section.
The 3D Viewport has two keys that affect selection:
Select by Origin Ctrl
Selects objects by their origin rather than their geometry.
Selection Menu Alt
Shows a menu in case there are multiple objects under the mouse cursor, making it easier to select the one you want.
These keys can be combined to get a selection menu based on object origins.
The mode-specific selection pages are listed below.