This is the 9th most frequent Greek word.
των
"Their" or "of the" (genitive plural definite article in Greek).
Here, "των" is used to show the relationship of possession between "success" and "students" in a genitive plural context.
Η επιτυχία των μαθητών ήταν εντυπωσιακή.
The success of the students was impressive.
In this sentence, "των" again serves as a genitive plural article denoting possession or relation between "efforts" and "employees."
Οι προσπάθειες των εργαζομένων ήταν αξιοθαύμαστες.
The efforts of the employees were admirable.
The word "των" indicates possession in this genitive plural construction, linking "friends" to "the house" to indicate ownership.