This is the 379th most frequent Persian word.
هایی
The Persian word "هایی" is a plural or attributive suffix meaning "ones" or "some."
In this sentence, 'هایی' is used as a suffix to indicate the plural form of the noun 'کتاب' (book), referring to multiple books.
کتابهایی که خواندم به من کمک کردند.
The books that I read helped me.
Here, 'هایی' is also a plural suffix, modifying 'فرد' (individual) to indicate multiple individuals.
افرادی که برای مهمانی دعوت شدند، آمدند.
The individuals who were invited to the party came.
In this example, 'هایی' is a plural suffix attached to 'چیز' (thing), referring to multiple things.