A mode is when the same gesture causes different actions to be performed. The flashlight with a single button is an example of an everyday object which uses modes. You push the button and the flashlight illuminates, push the same button again and the flashlight turns off. Modes are common in everyday objects and computer interfaces.
Despite their common nature, modes exhibit a variety of problems. The first is communicating which state an object is currently in. If the flashlight is in your backpack, you have no way of telling whether it is on or off. Another problem inherent with modes is labeling. Try to label the single button on a flashlight. If you had a small LED display next to the button, you might have it say "On" when the flashlight was off, to describe the effect pressing the button would have. However, this "On" could also be interrepted as the current state of the object. Another suggesstion might be labeling the button "On/Off." This is also unclear. Does the button turn the flashlight on and off at the same time? What is the exact meaning of the slash in the label? There are many ambiguities.