This is the 664th most frequent Finnish word.
opiskelijoiden
"Of the students" (possessive form).
The form 'opiskelijoiden' is the plural possessive form, indicating that the project belongs to the students.
Opiskelijoiden projekti on edennyt hyvin.
The students' project has progressed well.
Here, 'opiskelijoiden' is in the genitive case to show possession: the achievements of the students.
Olen ylpeä opiskelijoiden saavutuksista.
I am proud of the students' achievements.
In this sentence, 'opiskelijoiden' is in the genitive plural case to indicate possession by the students.