die Absperrung
barrier
A barrier, fence, or tape used to make a certain area inaccessible or to control access.
Die Polizei hat um den Unfallort eine Absperrung errichtet.
The police set up a barrier around the accident site.

barrier / closure
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barrier
A barrier, fence, or tape used to make a certain area inaccessible or to control access.
Die Polizei hat um den Unfallort eine Absperrung errichtet.
The police set up a barrier around the accident site.

'Absperrung' (barrier / closure) is a noun derived from the separable verb 'absperren' (to block off). The ending '-ung' turns the verb into a feminine noun that can refer both to the action and to its result, the barrier.
Die Polizei musste die Straße absperren.
The police had to block off the street.
The context tells you whether the action or the object is meant. Verbs like 'errichten' (to erect / set up) or 'aufstellen' (to set up), and prepositions like 'hinter' (behind), point to the barrier. Time expressions or a genitive object, such as 'die Absperrung der Brücke' (the closure of the bridge), refer to the action.
Die Zuschauer mussten hinter der Absperrung warten.
The spectators had to wait behind the barrier.
Certain verbs are often used in connection with the barrier: you can 'errichten' (erect / set up), 'aufbauen' (set up), 'durchbrechen' (break through), or 'entfernen' (remove) an 'Absperrung' (barrier).
Für das Konzert wurde eine große Absperrung errichtet.
A large barrier was set up for the concert.
fuse / backup / safety
'die Sicherung' and 'die Absperrung' can both occur around a dangerous or protected area. 'Absperrung' means a barrier or the act of blocking off an area, for example with tape, a fence, or barriers. 'Sicherung' is more general: an area is protected or guarded, and a barrier can be part of that. The words can be confused when police or construction workers secure a place. If you mean the visible barrier, 'Absperrung' is more precise. If you mean the whole protective setup, 'Sicherung' fits.

Am Abend steht eine Absperrung vor dem Supermarkt, weil dort gebaut wird.
In the evening, there is a barrier in front of the supermarket because construction work is taking place there.
Die Sicherung des Eingangs ist heute Aufgabe des Sicherheitsdienstes.
Securing the entrance is the security service's job today.