This is the 5405th most frequent Polish word.
strajkujących
"Strajkujących" means "of those striking" or "striking (people)."
The word 'strajkujących' is used here as a plural, genitive case, present participle meaning 'those who are striking' to describe the postal workers.
Strażacy dołączyli do strajkujących pracowników poczty.
The firefighters joined the striking postal workers.
In this sentence, 'strajkujących' denotes the possessive form in the genitive case referring to 'the strikers,' emphasizing they belong to a group being discussed.
Słuchaliśmy przemowy lidera strajkujących.
We listened to the speech of the leader of the strikers.
Here, 'strajkujących' is in the genitive case and describes the people 'those striking' being referred to in the picture.