(bÄt) n. 1. An agreement usually between two parties that the one who has made an incorrect prediction about an uncertain outcome will forfeit something stipulated to the other; a wager: made a bet that it would stop raining before 2:00. 2. An amount or object risked in a wager; a stake: a bet of $50.
1 billion seconds is a significant birthday or anniversary, being about 4 months shy of 32 years. 1 billion seconds is 31 years, 251 days, 13 hours, 34 minutes, 54.7843 seconds. But note that these are 365-day years, so you have to adjust for leap years. Remember, a leap year adds 1 day at the end of February on years that are divisible by 4, unless they're also divisble by 100, except when it's also divisible by 400.
Here's how I came up with that figure: To count to 1 billion would take 999,999,999 seconds, because the timer would start as soon as the person says one, one second would have passed when the person says two, and so on. [Thanks to Jacques de Wet for this observation.] Now, there are 31557600 seconds in one year (seconds*minutes*hours*days).