So what does it mean? 
After stopping:-

20 minutes

Blood pressure and pulse rate return to normal.

8 hours

Nicotine and carbon monoxide levels in blood reduce by half, oxygen levels return to normal.

24 hours

Carbon monoxide will be eliminated from the body.
Lungs start to clear out mucus and other smoking debris.

48 hours

There is no nicotine left in the body.
Ability to taste and smell is greatly improved.

72 hours

Breathing becomes easier.
Bronchial tubes begin to relax and energy levels increase.

2 - 12 weeks

Circulation improves.

3 - 9 months

Coughs, wheezing and breathing problems improve as lung function is increased by up to 10%.

1 year  

Risk of a heart attack falls to about half that of a smoker.

10 years

Risk of lung cancer falls to half that of a smoker.

15 years

Risk of heart attack falls to the same as someone who has never smoked.