حلقة النقاش بعد الكلمة الرئيسية.

Because Arabic often uses a nominal sentence in the present tense without a separate word for is/are.

So حلقة النقاش بعد الكلمة الرئيسية naturally means:

The discussion panel is after the keynote speech.

Arabic only needs an explicit verb here if you want a different time, such as the past or future:

• كانت حلقة النقاش بعد... = The discussion panel was after...
• ستكون حلقة النقاش بعد... = The discussion panel will be after...

It is an iḍāfa construction, often called a construct phrase.

It is built like this:

• حلقة = circle, session, panel
• النقاش = the discussion

Together, حلقة النقاش means something like:

• the discussion panel
• the panel discussion
• the discussion session

Literally, it is closer to the circle/session of discussion, but English usually translates it more naturally.

In an iḍāfa, the first noun usually does not take الـ. The definiteness of the whole phrase comes from the second noun.

So:

• حلقة نقاش = a discussion panel or discussion panel
• حلقة النقاش = the discussion panel

Even without الـ on حلقة, the whole phrase is definite because النقاش is definite.

Because ة (taa marbuuTa) is usually pronounced:

• like -a / -ah when you stop on the word by itself
• like -t when the word is connected to what follows, especially in an iḍāfa

So:

• by itself: حلقة → roughly ḥalaqa
• in this phrase: حلقة النقاش → roughly ḥalaqat an-niqāsh

The same thing can happen with other words ending in ة when they are grammatically connected.

Yes, you can think of بعد here as meaning after.

It introduces the time phrase:

• بعد الكلمة الرئيسية = after the keynote speech

In traditional Arabic grammar, بعد is often treated as a time adverb/ẓarf that is linked to the noun after it. For a learner, the important point is:

• بعد = after
• the following noun phrase is grammatically dependent on it

So the structure is straightforward:

• حلقة النقاش = the discussion panel
• بعد الكلمة الرئيسية = after the keynote speech

Because كلمة can mean more than just word. In formal Arabic, it can also mean:

• speech
• address
• remarks

This is especially common in event or conference language.

So الكلمة الرئيسية does not mean the main word here. It means something like:

• the keynote speech
• the keynote address

This is a normal and very common usage.

Because الرئيسية is an adjective describing الكلمة, and Arabic adjectives must agree with the noun they describe.

الكلمة is:

• feminine
• singular
• definite

So the adjective must also be:

• feminine
• singular
• definite

That gives:

• الكلمة الرئيسية

Also, in Arabic, adjectives normally come after the noun, not before it.

A very useful clue is the use of الـ.

In الكلمة الرئيسية

Both words have الـ:

• الكلمة
• الرئيسية

That is what you expect in a noun + adjective phrase, because the adjective matches the noun in definiteness.

In حلقة النقاش

Only the second word has الـ:

• حلقة
• النقاش

That is the typical pattern of an iḍāfa.

So:

• حلقة النقاش = construct phrase / iḍāfa
• الكلمة الرئيسية = noun + adjective

This contrast is actually a very good example of the difference between the two structures.

A fully vowelled version is:

حَلَقَةُ النِّقاشِ بَعْدَ الكَلِمَةِ الرَّئِيسِيَّةِ

A rough transliteration is:

ḥalaqatu n-niqāshi baʿda al-kalimati r-raʾīsiyyati

A few useful pronunciation notes:

• النِّقاش is pronounced an-niqāsh, because ن is a sun letter
• الرَّئيسية is pronounced ar-raʾīsiyya, because ر is also a sun letter
• حلقة is pronounced with -t here because it is in an iḍāfa

In normal unvowelled reading, many speakers would not pronounce all the case endings fully, but this is the careful MSA form.