What is a single-flash transistor-and-capacitor circuit actually called?
Although there are more than a few ways in which to create such a circuit; in general these are called &quot;monostable multivibrators.&quot;  These can also be called a &quot;one-shot&quot; or &quot;monoflop.&quot;
A &quot;multivibrator&quot; is an analog circuit which changes output state (emulating digital behavior) based on an input change. That input may be external to the circuit, preset to a defined state, or be the output of another multivibrator, creating several different possible behaviors.
The original inventors called these &quot;multivibrators&quot; because the output, due to using analog circuitry, was impure (imprecise) and thus, rich in harmonics (noise), especially at higher frequencies.
There are several variants of multivibrator, such as &quot;astable&quot; and &quot;bistable&quot;.  The differences are:

Astable: no inputs, unstable in either state; oscillates back-and-forth.




simulate this circuit &ndash; Schematic created using CircuitLab

Monostable: one input, stable in one state only. Applying input causes output change, but output always reverts to original state after a delay. These are handy to &quot;clean-up&quot; a noisy switch for example.




simulate this circuit

Bistable: two inputs, stable in both output states. Applying an input change causes the output to change, and it will stay that way until the other input change happens. Commonly called &quot;set&quot; and &quot;reset&quot;, which is a primitive form of latch or flip-flop.




simulate this circuit
There should be a &quot;simulate&quot; button under each of these... give them a try!