This is the 53rd most frequent Persian word.
کردند
"Did" or "they did."
Here, 'کردند' is used as the third-person plural past tense of the verb 'کردن', meaning 'to do or to perform'. It signifies an action completed in the past by a group.
آنها دیروز یک جشن برگزار کردند.
They organized a celebration yesterday.
In this sentence, 'کردند' forms the past tense of 'مطالعه کردند', meaning 'they studied'. It conveys an academic or intellectual activity done by the students.
دانشآموزان به کتابخانه رفتند و مطالعه کردند.
The students went to the library and studied.
The word 'کردند' complements 'خریداری', forming 'خریداری کردند', which translates to 'they bought'. It denotes a completed purchasing action by the parents.