In general: price put on the time an investor has to wait until an investment matures, as determined by calculating the Present Value of the investment at maturity. See also Yield to Maturity.
Options: that part of a stock option Premium that reflects the time remaining on an option contract before expiration. The premium is composed of this time value and the Intrinsic Value of the option.
Stocks: difference between the price at which a company is taken over and the price before the Takeover occurs. For example, if XYZ Company is to be taken over at $30 a share in two months, XYZ shares might presently sell for $28.50. The $1.50 per share difference is the cost of the time value those owning XYZ must bear if they want to wait two months to get $30 a share. As the two months pass, the time value will shrink, until it disappears on the day of the takeover. The time that investors hold XYZ has a price because it could be used to invest in something else providing a higher return. See also Opportunity Cost.