This is the 1194th most frequent Russian word.
желающих
"Желающих" means "those wishing" or "those who want."
In this sentence, "желающих" is the genitive plural form of the active participle "желающий," which means "wanting" or "desiring." It is used here to refer to people who wish to take seats in the bus in an attributive manner.
Мест в автобусе хватило для всех желающих.
There were enough seats in the bus for all those who wanted.
Here, "желающих" operates in the dative plural form, referring to the group of individuals wishing to participate. It is substantive, serving the role of 'those who wish' as a noun.
Для участия в конкурсе приглашаются все желающие.
Everyone who wants to participate in the competition is invited.
In this instance, "желающим" is in the dative plural form, referring to individuals who express interest in receiving information, indicating recipients in the action.