This is the 783rd most frequent Finnish word.
pörssin
"Of the stock exchange."
In this sentence, "pörssin" is in the genitive case, indicating possession, and it refers to 'the stock market.' The word 'pörssin' specifies that the indices belong to the stock market.
Pörssin kurssit nousivat tänään huomattavasti.
The stock market's indices rose significantly today.
Here, 'pörssin' is in the genitive case, connected to 'olevan,' indicating possession or association. It specifies the thing (the stock market) that is open.
Kuulin uutisista pörssin olevan auki poikkeuksellisesti sunnuntaina.
I heard from the news that the stock market is exceptionally open on Sunday.
In this sentence, 'pörssin' again shows possession, describing that the highest point belongs to the stock market.