Step 1: Understand the question.
We must say what pressing Ctrl plus Z does in Microsoft Word.
Step 2: Recall common shortcuts.
Keyboard shortcuts let users act quickly. Ctrl plus Z is one of the most used shortcuts in almost every program.
Step 3: Meaning of Undo.
Undo reverses the last action you did. If you typed by mistake or changed formatting, Undo takes you one step back.
Step 4: Match the key to the action.
In Word, Ctrl plus Z performs Undo. The document returns to how it was just before your last action.
Step 5: Reject the others.
Redo is Ctrl plus Y, Save is Ctrl plus S, and Delete uses the Delete key. None of these is Ctrl plus Z.
Step 6: Conclude.
So Ctrl plus Z means Undo, which is option 2.
\[ \boxed{\text{Undo}} \]