This is the 3143rd most frequent Arabic word.
اللذين
"اللذين" means "those who" (referring to two masculine individuals).
The word 'اللذين' is used here to refer to the male students (plural masculine noun) who performed the action of passing the exam. It is a relative pronoun.
الطلاب اللذين نجحوا في الامتحان سعداء.
The students who passed the exam are happy.
The word 'اللذين' is used here to describe the team members as the doers of the action of winning the match. It connects the subject 'team members' to their action.
الفريق الرياضي اللذين فازوا بالمباراة يحتفل الليلة.
The sports team who won the match are celebrating tonight.
In this sentence, 'اللذين' links the noun 'children' with their characteristic or action of loving reading.