This is the 5771st most frequent German word.
brief
Letter.
Here, 'Brief' is used as a noun meaning 'letter' in the sense of a written communication.
Ich habe gestern einen Brief geschrieben.
I wrote a letter yesterday.
In this instance, 'brief' is an adjective borrowed from English used to describe something concise or short in length.
Die Rede war sehr brief und auf den Punkt.
The speech was very brief and to the point.
In this example, 'Brief' functions as a component of a compound noun indicating a specific type of document.