An analogy to define the term half-life?

Hey there!:

The half life of a radioactive element is the time interval in which a sample of this element reduces to half. This interval of time is also called the period of disintegrating.As radioactive elements disintegrate, in the course of time, their quantity and activity are reducing and consequently the amount of energy emitted by it, due to radioactivity, is also reduced.

hope this helps!

If you had 1,000 pennies and threw them into the air, you would expect 500 to land heads up and 500 to land with tails up. Now, imagine someone took all of the tails up pennies, leaving with you 500 left. You throw the remaining pennies in the air, and again about half of them will land heads up.
Now, assuming each flip is considered a half life, that heads act as reactants and tails are products that go away, it acts just as a first order reaction. In each flip you end up with half of what you had before, no matter how many it was!