A story within a story, also referred to as an embedded narrative, is a literary device in which a character within a story becomes the narrator of a second story (within the first one). Multiple layers of stories within stories are sometimes called nested stories.

In mathematics and group theory, a block system for the action of a group G on a set X is a partition of X that is G-invariant. In terms of the associated equivalence relation on X, G-invariance means that

Dutch symphonic metal band Within Temptation have released seven studio albums, three live albums, four extended plays and 26 singles.

A system of signalling on railroads. The essence of the system consists in having signal posts or stations all along the road at distances depending on the traffic. The space between each two signal posts is termed a block. From the signal posts the trains in day time are signalled by wooden arms termed semaphores, and at night by lanterns. The arms may be moved by hand or by automatic mechanism depending in part on electricity for carrying out its functions. Thus in the Westinghouse system the semaphores are moved by pneumatic cylinders and pistons, whose air valves are opened and shut by the action of solenoid magnets, q. v. The current of these magnets is short circuited by passing trains, so as to let the valves close as the train passes the signal post. The block system causes the semaphore to be set at "danger" or "caution," as the train enters the next block. Then the following train is not allowed to enter the block until the safety signal is shown. The Westinghouse system provides for two semaphores on a post, one indicating "danger" as long as the train is on the next block; the other indicating "caution" as long as the train is on the next two blocks. The rails form part of the circuit, their joints being bridged by copper wire throughout the block, and being insulated where the blocks meet.

Atrioventricular block (AV block) is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatrial node (SA node) produces an electrical signal to control the heart rate.

In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks. They are specified elementary components in the design of many cryptographic protocols and are widely used to encrypt large amounts of data, including in data exchange protocols. It uses blocks as an unvarying transformation.

A city block, residential bloc urban block, or simply block is a central element of urban planning and urban design.

In mathematical finite group theory, a block, sometimes called Aschbacher block, is a subgroup giving an obstruction to Thompson factorization and pushing up. Blocks were introduced by Michael Aschbacher.