What’s the difference between double hung and single windows?

Double hung windows are based on the iconic design of single hung windows, with one major difference, the number of operable sashes. A double hung window has two operable or moveable sashes, whereas a single hung window has one fixed/non-operable sash and one operable or moveable sash. A double hung window offers better ventilation than a single hung window as you can open either the top sash, the bottom sash or both.