Undo

It cancels the previous operation.

Redo

It cancels [Undo].

Select All

It selects all vertices, lines, and faces.

Invert all the selection of vertices

It inverts the selected condition of all vertices.

Invert al the selection of faces

It inverts the selected condition of all faces.

Unselect all

It unselects all vertices, lines, and faces.

Select all in a current object

It selects all vertices, lines, and faces of a current object.

Before		After

Invert all the selection of vertices in a current object

It inverts all the selection of vertices in a current object.

Invert all the selection of faces in a current object

It inverts all the selection of faces in a current object.

Unselect All in a current object

It unselects all vertices, lines, and faces of a current object.

Select all the faces in a current Material

It selects all the faces that the current material is assigned to.

Unselect all the faces in a current material

It unselects all the faces that the current material is assigned to.

Lock selection

When you check this, you cannot select or unselect while using [Select], [Move] command and so on. But it can be used for a part of commands and not for all commands. And it does not affect the operation on Menu.

The ON/OFF status is shown on the status bar.