entfallen
to be canceled
Not to take place; to be canceled or called off.
Wegen Krankheit der Lehrerin ist der Unterricht heute entfallen.
Because the teacher is ill, class was canceled today.

to be canceled / to slip one's mind / to fall to
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to be canceled
Not to take place; to be canceled or called off.
Wegen Krankheit der Lehrerin ist der Unterricht heute entfallen.
Because the teacher is ill, class was canceled today.

'Entfallen' (to be canceled/to slip one's mind/to fall to) is an inseparable verb. The prefix 'ent-' remains attached to the verb stem in all sentence forms and tenses and is not placed at the end of the sentence.
Ich hoffe, dass die Prüfung morgen nicht entfällt.
I hope the exam isn't canceled tomorrow.
The perfect tense of 'entfallen' (to be canceled/to slip one's mind/to fall to) is always formed with the auxiliary verb 'sein' (to be). This is because the verb describes a change or a disappearance.
Die letzte Stunde ist gestern entfallen.
The last class was canceled yesterday.
In the meaning 'vergessen werden' (to be forgotten), 'entfallen' (to slip one's mind) is used with the dative. The person who forgets something is in the dative, while the forgotten information is the subject of the sentence.
Mir ist die Adresse entfallen, kannst du sie mir nochmal sagen?
The address has slipped my mind; can you tell it to me again?
When 'entfallen' means that a share falls to something, it is always used with the preposition 'auf' and the accusative. The structure is: share + entfallen + auf + whole.
Von den Einnahmen entfällt ein Drittel auf die Steuern.
Of the revenue, one third falls to taxes.
to forget
'vergessen' and 'entfallen' are similar when a piece of information is no longer in your memory. 'vergessen' is the normal everyday word and fits in almost all situations. 'entfallen' sounds somewhat more formal or polite and is often used with the dative: 'Mir ist der Name entfallen' (the name has slipped my mind). It often describes a brief moment when you no longer know something. Important: 'entfallen' can also mean 'to be canceled', but that is a different meaning and not the same as 'vergessen'.

Nach der Besprechung ist mir der genaue Preis entfallen.
After the meeting, the exact price slipped my mind.
Hast du die Adresse von Frau Becker vergessen?
Have you forgotten Ms. Becker's address?