This term would cover different types of protective devices (GFCI, circuit breaker, etc.).

I believe it's the theory behind protection rather than any specific devices...

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Note added at 58 mins (2020-04-30 03:54:53 GMT)
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"Prinzip der Fehlerstrom-Schutzschaltung"

This is referring to the concept as opposed to a specific device for fault currents.

In the USA, this is what this thing is called. The outlets are mandatory in every bathroom, as far as I know.
This link says:
The ground-fault circuit interrupter, or GFCI, is a fast-acting circuit breaker designed to shut off electric power in the event of a ground-fault within as little as 1/40 of a second.

So, dropping a toaster into the full bathtub will no longer send Uncle Joe to his last reward, regardless of what you see in the movies.

Please distinguish "Schutzschalter" and "Schutzschaltung". Teh latter is no device, but an circuit.

protection circuit die Schutzschaltung Pl.: die Schutzschaltungen
protective circuit [ELEKT.] die Schutzschaltung Pl.: die Schutzschaltungen
https://www.proz.com/kudoz/german-to-english/electronics-ele...

"protection circuit" About 3.400.000 results (0,50 seconds)
"protective circuit" About 571.000 results (0,46 seconds)

Area Electrical accessories / Circuit-breakers and similar equipment for household use
IEV ref 442-05-19
Symbol IΔ
en residual current
RMS value of the vector sum of the instantaneous values of the currents flowing through the main circuit of the residual current device
de Fehlerstrom, m
http://www.electropedia.org/iev/iev.nsf/display?openform&iev...

Area Electrical accessories / Circuit-breakers and similar equipment for household use
IEV ref 442-05-02
en residual current device, RCD
mechanical switching device or association of devices designed to make, carry and break currents under normal service conditions and to cause the opening of the contacts when the residual current attains a given value under specified conditions
de Fehlerstrom-Schutzeinrichtung, f
http://www.electropedia.org/iev/iev.nsf/display?openform&iev...

The additional equipotential link between the support element and the main protection circuit. (whether this is created using exposed conductive parts or conductors] must be sized according to the maximum current, which is equal to the sum of the currents of each of the devices fixed on, in accordance with the table on page 34.
https://www.legrand.be/sites/default/files/guides_techniques...

If the power generator is equipped with a residual-current protective circuit, the star point of the generator must be connected to the casing of the power generator, and via the earthing screw to a suitable potential equalisation conductor.
http://www.bsenet.de/Geko/Bedienungsanleitung-Geko-2801.pdf

residual-current protective circuit -- FehlerstromSchutzschaltung {f} [electr.]
https://books.google.de/books?id=cT1WDwAAQBAJ&pg=PT12511&lpg...

The protective earthing measure can be problematic however, since the rapid activation of the overcurrent protective device requires extremely high currents, which in turn require the lowest possible earthing resistances. If stronger electric circuits are required, it will be necessary to resort to a Residual Current Protective Device. The strength of the release current is also dependent on the earthing conditions where the residual-current protective circuit is concerned.
https://www.kollmorgen.com/de-de/node/1301/

The type of protection used is the residual-current protective circuit (tripping current 30 mA).
https://www.augsbow.de/wp-content/uploads/2019/05/ABO20-10_P...

Ensure that the device is protected via a residual-current protective circuit with a rated residual current of maximum 30Ma.
https://www.google.com/search?client=firefox-b-d&biw=855&bih...

Also:

Fehlerstromschutzschaltung f / current-operated earth-leakage protection, protection by residual current-operated protective device
(Budig, Fachwörterbuch Elekttrotechnik und Elektronik)

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Note added at 4 days (2020-05-04 09:26:53 GMT) Post-grading
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Zwischenzeitlich habe ich auch eine Beschreibung dieser Schutzschaltung im Internet gefunden, die meine Aussagen (vgl. Diskussion) voll bestätigen:

VII Fehlerspannungs(FU)-Schutzschaltung.
Die Fehlerspannungsschutzschaltung schaltet den überwachten Verbraucher ab, wenn durch Isolationsfehler die Fehlerspannung auf 65 V ansteigt.
Die Fehlerspannungsspule F ist durch einen Schutzleiter SL mit den zu überwachenden Metallteilen des Verbrauchers (Motorgehäuse) verbunden. Die andere Spulenseite liegt über einen Hilfserdungsleiter D an einer Hilfserde RH. Wenn die Berührungsspannung zu hohe Werte annimmt, wir die Spule F erregt und löst über ein Schaltschloß den Fehlerspannungsschutzschalter aus und schaltet den Körperschluß ab. Die Abschaltung erfolgt allpolig; auch der Nulleiter wird, falls er angeschlossen ist, abgetrennt.
Abb. 143. Fehlerspannungs(FU)-Schutzschaltung.
https://books.google.de/books?id=_VOyBgAAQBAJ&pg=PA132&lpg=P...
Anm.: Das Schaltbild zeigt die gleiche Konfiguration wie in meinem Fachbuch.

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Note added at 5 days (2020-05-05 10:55:26 GMT) Post-grading
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Bitte den Nachtrag nicht beachten! Er gehört zu "FU-Schutzschaltung" und wurde irtümlicherweise hier gepostet.