Toast is sliced bread that has been browned by radiant heat. The browning is the result of a Maillard reaction altering the flavor of the bread and making it crispier in texture. The firm surface is easier to spread toppings on and the warmth can help spreads such as butter reach their melting point. Toasting is a common method of making stale bread more palatable. Bread is commonly toasted using devices specifically designed for such, e.g., a toaster or a toaster oven. Toast may contain more acrylamide, caused by the browning process, which is suspected to be a carcinogen. However, claims that acrylamide in burnt food causes cancer have not been proven.

Butter or margarine, and sweet toppings, such as jam, marmalade or jelly, are commonly spread on toast. Regionally, savory spreads, such as peanut butter or yeast extract, may also be popular. Toast may accompany savory dishes such as soups or stews, or it can be topped with ingredients like eggs or baked beans to make a light meal. Toast is a common breakfast food. A sandwich may also use toasted bread.

The word toast comes from Latin torrere 'to burn'. In German, the term (or sometimes Toastbrot) also refers to the type of bread itself, which is usually used for toasting.

One of the first references to toast in print is in a recipe for Oyle Soppys (flavoured onions stewed in a gallon of stale beer and a pint of oil) from 1430. Toasting was likely first used to increase the edibility of bread that had become slightly stale. In the 1400s and 1500s, toast was discarded or eaten after it was used as a flavoring for drinks. In the 1600s toast was still thought of as something to be put into drinks. William Shakespeare in his play The Merry Wives of Windsor (1602) gives John Falstaff the line "Go fetch me a quart of sack; put a toast in't." Toast has been used as an element of American haute cuisine since at least the 1850s.

Bread sold ready-sliced is commonly used in modern preparations; some of these specifically market their suitability for toasting.^{[citation needed]}

Toasting is a cooking process that depends on the occurrence of the Maillard reaction on the surface of the bread. The Maillard reaction only occurs when foods reach temperatures in excess of 155 °C (310 °F). Generally the toasting process is complete once the surface temperature of the toast is between 155 °C and 190 °C, depending on the desired surface color. Above these temperatures, toast will exude a burnt odor, which is associated with pyruvic aldehyde until it eventually ignites at 250 °C (482 °F).

In a modern home kitchen, toast is usually made in a special-purpose electrical appliance, a toaster. Sliced bread is placed into the slots on the top of the toaster, the desired degree of toasting is set, and a lever is pushed down to expose the bread to the heated elements. The toast is popped up when it is ready. Bread toasted in a conventional toaster can "sweat" when it is served (i.e. water collects on the surface of the cooled toast). This occurs because moisture in the bread becomes steam while being toasted due to heat and when cooled the steam condenses into water droplets on the surface of the bread.

Bread can also be toasted under a medium-hot grill. Hotels, restaurants, and other food service locations often use a conveyor toaster, with heating elements both above and below the slices of bread, which are carried slowly between the red-hot elements by a metal conveyor belt, making toast continuously.