In options trading, Theta is a measure of the rate of decline in the value of an option due to the passage of time. Theta is often considered to be a "time decay" measure, as it estimates the amount by which the option's value will decrease as the expiration date gets closer.For example, if an option has a theta of -0.25, this means that the option's value is expected to decrease by $0.25 per day as the expiration date gets closer. If the option has a theta of -1.00, this means that the option's value is expected to decrease by $1.00 per day as the expiration date gets closer.Theta is an important factor to consider when trading options, as it can have a significant impact on the profitability of a trade. Options that have a high theta will have a faster rate of value decline, and therefore may not be as profitable as options with a lower theta.It's usually negative for call and positive for put options.