Step 1: List the common grades of ethanol by purity.
Rectified spirit is roughly $95.6\%$ ethanol mixed with water, denatured alcohol is ethanol deliberately spoiled with additives, and power alcohol is a fuel blend of alcohol with petrol.
Step 2: Notice none of these are $100\%$ pure.
Rectified spirit still carries about $4.4\%$ water that ordinary distillation cannot remove, denatured alcohol is intentionally impure, and power alcohol is a mixture with petrol, not pure ethanol at all.
Step 3: Identify the grade that is water free.
Only through special dehydrating techniques can the last trace of water be removed from rectified spirit, giving ethanol that is essentially $100\%$ pure.
Step 4: Name that grade.
This water free, fully pure form of ethanol is what chemists call absolute alcohol. \[ \boxed{\text{Absolute alcohol}} \]