This is the 807th most frequent Finnish word.
yhdistyksen
"Yhdistyksen" means "of the association" or "of the society" in English.
Here, 'yhdistyksen' denotes possessive usage, indicating 'of the association', showing ownership of the chairman to the association.
Hän on yhdistyksen puheenjohtaja.
She is the chairman of the association.
In this sentence, 'yhdistyksen' is a possessive form showing that the action plan belongs to the association.
Käsittelimme yhdistyksen toimintasuunnitelmaa kokouksessa.
We discussed the association's action plan at the meeting.
The word 'yhdistyksen' is in the genitive case here, showing possession, meaning 'of the association'.