Answer: Half life is the time in which a substance remains halve of its original amount. Mostly we use the term half life for radioactive substances.
For example:- Half life of carbon-14 is 5730 years. So, if we take 100 grams of carbon-14 then it will remain 50 grams in 5730 years. In next 5730 years, it will remain 25 grams.