the change in the premium of an option and compares it to a one-day change in
time-to-maturity. The longer an option’s time to expiration, the more valuable
an option is. High theta options are favored by option sellers because options
have a high rate of time decay.
The sensitivity of an option's market value relative to a change in the time to expiration. Theta is a measure of time decay and tends to grow larger as an option approaches expiration.