die Erklärung
explanation
Information or an account that makes a matter understandable or explains it.
Danke für deine Erklärung, jetzt verstehe ich das Problem.
Thanks for your explanation; now I understand the problem.

explanation / statement
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explanation
Information or an account that makes a matter understandable or explains it.
Danke für deine Erklärung, jetzt verstehe ich das Problem.
Thanks for your explanation; now I understand the problem.

The noun 'die Erklärung' (explanation / statement) is derived from the verb 'erklären' (to explain). The ending '-ung' turns the verb into a feminine noun.
Kannst du mir bitte die Grammatikregel erklären?
Can you please explain the grammar rule to me?
The verb used with 'Erklärung' (explanation / statement) gives a clue to the meaning. 'Eine Erklärung brauchen' (to need an explanation) points to an explanation. 'Eine Erklärung abgeben' (to make a statement) usually means an official statement. 'Die Erklärung für etwas sein' (to be the explanation for something) points to a reason.
Ich brauche eine einfache Erklärung für dieses physikalische Gesetz.
I need a simple explanation for this law of physics.
In the sense of an official statement, 'Erklärung' (statement) is often combined with adjectives such as 'öffentlich' (public), 'persönlich' (personal), or 'schriftlich' (written). The typical verb for this is 'eine Erklärung abgeben' (to make a statement).
Das Unternehmen hat eine offizielle Erklärung zu dem Vorfall veröffentlicht.
The company published an official statement about the incident.
When 'Erklärung' (explanation) refers to the cause or reason for something, it almost always appears with the preposition 'für' (for), followed by a noun in the accusative.
Gibt es eine logische Erklärung für dieses Phänomen?
Is there a logical explanation for this phenomenon?
reason / ground
'der Grund' and 'die Erklärung' can both say why something happened. 'der Grund' is the cause or occasion itself. 'die Erklärung' is often what someone says in order to make something understandable. But it can also mean the cause. That is why learners may confuse the words. A simple tip: 'der Grund' is the why. 'die Erklärung' is the answer to or description of the why. If you are asking about the cause, 'Grund' sounds very natural. If someone is explaining something, 'Erklärung' fits better.

Hannah gibt heute eine kurze Erklärung, warum der Termin verschoben wird.
Today Hannah gives a short explanation of why the appointment is being postponed.
Der Grund für ihre Verspätung war ein Unfall auf der Straße.
The reason for her delay was an accident on the road.