This is the 4782nd most frequent Russian word.
зарегистрированных
"Registered."
In this sentence, 'зарегистрированных' (of the registered) functions as an adjective modifying 'участников' (participants), indicating that these individuals have completed a registration process.
Число зарегистрированных участников увеличилось за год.
The number of registered participants has increased over the year.
Here, 'зарегистрированных' (registered) also serves as an adjective that describes 'посетителей' (guests), emphasizing their state of having undergone registration.
У нас есть список зарегистрированных посетителей.
We have a list of registered guests.
In this case, 'зарегистрированных' (registered) once again acts as an adjective qualifying 'пользователей' (users), denoting those who have signed up on the website.