Step 1: Start from quicklime.
Calcium oxide, $CaO$, is commonly called quicklime, made by strongly heating limestone.
Step 2: Add water to quicklime and see what forms.
\[ CaO + H_2O \to Ca(OH)_2 + \text{heat} \] This reaction is called slaking, since quicklime is being slaked or quenched with water, and the product, calcium hydroxide, naturally inherits the name slaked lime.
Step 3: Rule out the other names.
Calcium oxide itself is quicklime, not slaked lime. Calcium carbonate is limestone or chalk. Sodium hydroxide is caustic soda, a completely different metal's hydroxide. None of these fit the term slaked lime.
Step 4: Conclude.
Calcium hydroxide is known as slaked lime. \[ \boxed{Ca(OH)_2 = \text{Slaked lime}} \]