Define the "half-life" of a radioisotope

The amount of time it takes for 1/2 of it to decay or dissapear

this is liike compound interest because it takes the same amount of time to decay 1/2 of it, regardless of the amount

example

lets say half life of element x is 1 year
if yo has 32 grams, after  1 year, it decays to 16g
2 years decays to 8
3 years decays to 4
4 years decays to 2
5 years decays to 1
etc

hope this helps (I'm not the best at chem)