A window of opportunity is a short time period during which an otherwise unattainable opportunity exists. After the window of opportunity closes, the opportunity ceases to exist. Since good deals on real estate, business offers, etc. do not exist forever, the window of opportunity is the ideal time to act.

An example of a window of opportunity is the initial public offering (IPO) of a stock. With some rapidly rising stocks, such as Google, there is a small window of opportunity during its IPO before its price might significantly rise. A window of opportunity also exists when there is a temporary stock mispricing in the market, which will be corrected as soon as traders become aware.