A window was an opening through which a view could be observed.
Shop windows were used to display merchandise. (PROSE: Rose) During the Nestene's attempted invasion of Earth in the 1970s, Auton shop window dummies came to life, broke out of the windows and started killing people. (TV: Spearhead from Space)
In the 1920s, the Doctor met Nellie Melba and learned her party trick of shattering glass with a high-pitched note. The Fourth Doctor used it on Delta III to shatter a window, allowing rain to dampen vines constricting him, Romana I and Rohm-Dutt. (TV: The Power of Kroll)
Time windows could be created by pushing energy into a warp drive, as was done on the SS Madame de Pompadour. (TV: The Girl in the Fireplace) The Doctor's TARDIS was also capable of opening time windows. (TV: Death Is the Only Answer)
When the newly regenerated Twelfth Doctor and Clara Oswald were staying with the Paternoster Gang, Strax delivered a copy of The Times by throwing it through a window, hitting Clara in the head. (TV: Deep Breath)