Less is the comparative form of little. It is used especially before uncountable nouns. Fewer is the comparative of few. It is used before plural nouns. For example:

Example :
1. I missed less work this year than last.
2. No fewer than fifty students were selected.
3. There are no less than five liters of water in the bottle.
4. Fewer than five children live in this apartment building.
5. We wear less clothing in hot weather.