das Thema
topic
The subject or central content of a conversation, text, film, or event.
Das Thema der heutigen Konferenz ist die Digitalisierung der Arbeitswelt.
The topic of today's conference is the digitalization of the working world.

topic / theme
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topic
The subject or central content of a conversation, text, film, or event.
Das Thema der heutigen Konferenz ist die Digitalisierung der Arbeitswelt.
The topic of today's conference is the digitalization of the working world.

Certain prepositions are used with 'Thema' (topic/theme). You talk 'über' a topic (accusative), comment 'zu' a topic (dative), or stay 'beim' topic (dative).
Wir haben lange über dieses Thema diskutiert.
We discussed this topic for a long time.
Common verbs combined with 'Thema' are 'ein Thema ansprechen' (to bring up a topic), 'ein Thema behandeln' (to deal with a topic), and 'das Thema wechseln' (to change the topic).
Er hat in der Besprechung ein wichtiges Thema angesprochen.
He brought up an important topic in the meeting.
The expression 'vom Thema abkommen' (to get off topic) is a fixed idiom. The opposite, meaning to stay with the original subject of conversation, is expressed with 'beim Thema bleiben' (to stay on topic).
Entschuldigung, ich bin kurz vom Thema abgekommen.
Sorry, I briefly got off topic.
When 'Thema' is used in connection with music, composers, a symphony, or a melody, it always refers to the musical idea.
Der Komponist variiert das Hauptthema im gesamten Stück.
The composer varies the main theme throughout the entire piece.
question
'die Frage' and 'das Thema' can both relate to the content of a conversation or discussion. 'das Thema' is the broader area you are talking about, for example housing, sports, or work. 'die Frage' is more like a single point within that area that needs to be clarified or answered. Learners may confuse the words because you can discuss a question, and then it can feel almost like a topic. When you mean the general content, 'Thema' is more natural. When a decision or answer is missing, 'Frage' fits better.

Beim Training spricht er oft über das Thema gesunde Ernährung.
During training, he often talks about the topic of healthy eating.
In der Besprechung ist die Frage offen geblieben, wann das Projekt beginnt.
In the meeting, the question of when the project would begin remained open.