See: Theta Decay.
It sounds like what happens when you don't floss, but it actually refers to the way that the time value of a stock option decays or declines with time.
The closer to the expiration date, the smaller the time value of the option. (Time value: as in...if you had an option to buy KO for $50 when KO is today trading at $42, and that option expired in 2 weeks, it probably wouldn't be worth much, because the odds of KO trading much above $50 in the next 2 weeks is relatively low. But if you had Theta (or time) of 3 years before the option expired, then yeah, that option could be worth a ton.)
Example:
You sold puts on GOOG at $450 for $35 which expire in 4 months. The stock today is at $600. That is, you sold the right for someone to make you buy shares of GOOG at $450 any time between now and 4 months from now for 35 bucks. Things go along and, well, GOOG just stays pretty flat, doing a whole lot of nothing.
It's now 3 days before those put options expire (we've gone 3.9 months with a whole lot of nothing happening in GOOG). The stock is still around $600 a share. What are the odds it plummets $150+ in 3 days? Really low. So the value of those puts is almost fully expired—its Theta has decayed to just 3 days' worth of trading time, and it is highly likely you just collect your 35 bucks, walk away, and buy yourself a really nice burger at a Manhattan eatery.
Related or Semi-related Video
Finance: What is a Derivative?23 Views
finance a la shmoop what is a derivative? well it's derived it's a something taken
from something else like a derivative of hot weather is thirst a derivative of [Girl takes sip of glass of water on a beach]
hunger is well you know crankiness that's diva thing you get there...
derivative of a 1/32 quarterback rating in the NFL is like serious wealth yeah
yeah discount double shmoop yeah look for it be on there with aaron
and a derivative of a stock or bond or other security is a something which
derives its value based on the performance of that underlying security
there are basically two flavors of derivative put options ie the right to [Ice cream flavors appear]
sell a security at a given price over a given time period and a call option, ie
right to buy a security at a given price over a given time period
well the price of that option is derived from the price of the security and a few
other factors like strike prices and duration and all that stuff
colonel electric the downgraded new version of General Electric is trading [Colonel Electric appears in a suit]
for 25 bucks a share a derivative of its share price is sold in the form of a
call option with a $30 strike price expiring about 90 days from now on the
third Friday of the end of that month well investors pay a price albeit
probably a small one for the right to then pay 30 bucks a share for colonel [Call option appears for colonel electric]
electric at any time in the next 90 ish days until that option expires making the bet
that the stock will go well above 30 bucks a share in that time period that
call option is thus a derivative of the colonel electric primary stock price got
it if you really want to get personal well here's the ultimate form of
derivative [Baby laying down]
Up Next
Theta refers to either the amount of time left on a contract, or the sorority girl asking if you want to come to her mixer. The answer will always...
What is a put option? A put option is a type of contract that lets the investor sell shares of a stock at a certain price and within a window of ti...
What is a call option? A call option is a type of contract that lets the investor buy shares of a stock at a certain price and within a window of t...