This is the 12676th most frequent Polish word.
nieformalnego
"Nieformalnego" means "informal" in English.
Here, 'nieformalnego' is an adjective describing the type of meeting, emphasizing its casual nature.
Spotkanie miało charakter nieformalnego zebrania.
The meeting had the character of an informal gathering.
In this sentence, 'nieformalnego' modifies 'ubioru', describing the style as relaxed and not adhering to strict formality.
Styl nieformalnego ubioru pozwala na większą swobodę.
The style of informal clothing allows for greater comfort.
Here, 'nieformalnego' relates to 'stowarzyszenia', indicating the association is not formally structured or official.