tZero

"T equals zero." The beginning. When t or time is zero, the clock is just about to be started. Juuuust before the big bang. The race starts and we're off.

Or think: the opposite. You have a stock option, a call you've bought for $3 with $35 strike on a stock trading at $34.88 right now. Only four days left to its expiration, when t or Theta will then equal zero, and it'll likely expire as worthless.

See: Theta Decay.