ausführlich
detailed
With many details and very comprehensive; detailed and precise.
Der Zeuge hat den Vorfall sehr ausführlich geschildert.
The witness described the incident in great detail.

detailed
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detailed
With many details and very comprehensive; detailed and precise.
Der Zeuge hat den Vorfall sehr ausführlich geschildert.
The witness described the incident in great detail.

The word is derived from the verb 'ausführen' (to carry out / to explain in detail). When you 'ausführt' something, you present it in detail. 'Ausführlich' (detailed) therefore describes a result that is very detailed.
Bitte schreiben Sie eine ausführliche Zusammenfassung des Buches.
Please write a detailed summary of the book.
'Ausführlich' (in detail) can also be used as an adverb. It then describes how an action is carried out and usually stands directly with the verb.
Wir haben das Thema im Team ausführlich diskutiert.
We discussed the topic in detail as a team.
Common nouns combined with 'ausführlich' (detailed) are things that contain information: ein ausführlicher Bericht (a detailed report), eine ausführliche Erklärung (a detailed explanation), ein ausführliches Gespräch (a detailed conversation), or eine ausführliche Anleitung (detailed instructions).
In der E-Mail fand ich eine ausführliche Beschreibung des Problems.
In the email, I found a detailed description of the problem.
exact / precise
'genau' and 'ausführlich' can both have to do with good information. 'genau' emphasizes that something is precise and correct. So it is about exactness. 'ausführlich' emphasizes that something contains many details and is explained comprehensively. A text can be 'ausführlich' but still inaccurate if details are wrong. It can also be 'genau' but short. Learners confuse the words because detailed explanations are often also supposed to be precise. When it is about correctness and precision, 'genau' fits; when it is about lots of information, 'ausführlich' fits.

Im Bericht beschreibt er den Unfall ausführlich.
In the report, he describes the accident in detail.
Der Techniker misst die Länge sehr genau.
The technician measures the length very precisely.