The half life of a radioisotope is the time taken for the current level of radioactivity to drop to half that amount. Note that this means radioactive decay follows the curve of a decaying exponential. Oh, as mentioned, it is also somewhat of a revolutionary computer game. "As for the suit, I think you've earned it"
Carbon-14 has a half-life of 5,730 years. Let's say its radioactivity 'level' at time = 0 is 2. After around 5,730, its radioactivity will be 1, After a further 5,370 years its radioactivity will be 0.5, and after yet another half life, the radioactivty would be 0.25, and so on.