Glossary
An axis tripod appears in the viewports whenever you select one or more objects, to assist you visually in your transforms.
The tripod consists of three lines, labeled X, Y, and Z, and shows you three things:
The orientation of the tripod reveals the orientation of your coordinate system.
The location of the junction of the three axis lines shows you where your transform center is.
The highlighted red axis lines show you the axis or axes to which the transform is constrained. For example, if only the X axis line is red, you can move objects only along the X axis.
You can toggle the display of the axis tripod in all viewports by turning off Display World Axis, on the Viewports panel of the Preference Settings dialog.
See also