This is the 5548th most frequent Russian word.
получивших
"Получивших" means "those who received" or "having received."
In this sentence, 'получившими' is used as a past active participle, which describes the students who performed the action of receiving high grades.
Учебники были разделены между студентами, получившими высокие оценки.
The textbooks were distributed among students who received high grades.
Here, 'получивших' modifies the noun 'участников' and provides information about those participants who performed the action of receiving approval.
Письма для участников, получивших одобрение, отправятся завтра.
Letters for participants who received approval will be sent tomorrow.
In this usage, 'получивших' describes the people who completed the action of receiving awards.