ON

If a layer is ON it is visible. If a layer is OFF it is not visible.
Only layers that are ON can be edited or plotted.
(Warning: Objects on a Layer that is OFF can be accidentally erased even though they are invisible. When you are asked to select objects in the erase command, if you type ALL all objects will be selected; even the invisible ones. )

LOCK

LOCKED layers are visible but cannot be edited. They are visible so they will be plotted. (Locked layers cannot be selected by typing ALL. )

PLOT

This option prevents a layer from plotting even though it is visible.

FREEZE

Freeze and Thaw are very similar to On and Off. A Frozen layer is not visible.
A Thawed layer is visible. Only thawed layers can be edited or plotted.

Additionally:

1. Objects on a Frozen layer cannot be accidentally erased by typing All.

2. When working with large and complex drawings, freezing saves time because frozen layers are not regenerated when you zoom in and out.

Note: The next 2 are displayed only when you select a Layout tab.

CURRENT

Layers selected will be frozen in the current viewport only. Current means the active viewport. Only one viewport can be active at one time.
(Available in Paper Space only)

NEW

Layers selected will be frozen in the next viewport...