1. The time taken for the radioactivity of a specified isotope to fall to half its original value. the time required for any specified property (e.g. the concentration of a substance in the body) to decrease by half.
2. One of the best video games you could ever play along with Portal.
Scenario1: "Iodine-131 has a Half-life of 8.1 days"
Scenario2: I love Half-life, the story and gameplay is just mind blowing!