der Regelfall
normal case
The normal, usual, or typical case; the situation that normally occurs.
Im Regelfall erhalten Sie eine Antwort auf Ihre E-Mail innerhalb von 24 Stunden.
Normally, you will receive a response to your email within 24 hours.

normal case
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normal case
The normal, usual, or typical case; the situation that normally occurs.
Im Regelfall erhalten Sie eine Antwort auf Ihre E-Mail innerhalb von 24 Stunden.
Normally, you will receive a response to your email within 24 hours.

'Regelfall' (normal case) is made up of 'die Regel' (the rule) and 'der Fall' (the case). So it literally describes a case that corresponds to the rule—the normal, expected situation.
Dass die Sonne im Sommer scheint, ist der Regelfall.
That the sun shines in summer is the normal case.
This word is used almost exclusively in the fixed expression 'im Regelfall' (normally/as a rule). This expression means the same as 'normalerweise' (normally) or 'üblicherweise' (usually).
Die Bearbeitung Ihres Antrags dauert im Regelfall etwa zwei Wochen.
Processing your application normally takes about two weeks.
When a sentence begins with the expression 'Im Regelfall' (normally/as a rule), the conjugated verb comes directly after it in position 2.
Im Regelfall schließt das Geschäft um 18 Uhr.
Normally, the shop closes at 6 p.m.
rule / period
'in der Regel' and 'der Regelfall' both have to do with what normally happens. 'in der Regel' is a fixed expression and means 'usually' or 'normally'. 'der Regelfall' is a noun and refers to the normal or usual situation itself. You can confuse them because both talk about what is normal. The difference is mainly the form: 'in der Regel' is used like an adverb in a sentence, while 'der Regelfall' is used like a normal noun.

Eine kurze Antwort per E-Mail ist bei uns der Regelfall.
A short reply by email is the normal case for us.
In der Regel dauert der Termin beim Arzt nur zehn Minuten.
As a rule, the doctor's appointment only takes ten minutes.