Breakdown of Há uma reunião importante hoje à tarde.
Questions & Answers about Há uma reunião importante hoje à tarde.
In this sentence, há comes from the verb haver and means there is or there are.
So:
- Há uma reunião = There is a meeting
- Há duas reuniões = There are two meetings
In this use, haver is impersonal, so it does not agree with the noun after it.
This is a very common way to express existence in Portuguese, especially in neutral or more formal language.