This is the 3725th most frequent Russian word.
участник
Participant.
In this sentence, "участник" refers to someone who participates in a competition or organized event.
Он стал участником конкурса на лучший дизайн.
He became a participant in the competition for the best design.
Here, "участник" is used to describe a member of a collaborative group or team.
Каждый участник нашей команды вносит огромный вклад в проект.
Each member of our team contributes significantly to the project.
In this sentence, "участники" denotes those who are present and involved in a discussion or meeting.