Microwave ovens heat the molecules directly using radiation and are therefore much faster at heating than a regular oven or pan. The first microwave oven was available for domestic use in the late 1960s, starting the home use of microwaves. They are often used to heat leftover foods, ready-made meals, or other ingredients used for cooking such as butter, but can also be used to heat up other items such as heating pads.
Microwave oven penetration seems to have been stagnant since the mid 2000s in the United Kingdom. This may be attributable to the development of other kitchen appliances such as food steamers or immersion cookers.