This is the 4540th most frequent Catalan word.
opcional
Optional.
Here, 'opcional' is used as an adjective modifying the noun 'participació' to indicate that attending the event is not mandatory.
La participació en aquest esdeveniment és opcional.
Participation in this event is optional.
In this sentence, 'opcional' describes the assignments (noun 'tasques') as not obligatory, giving the choice of completing them.
Aquestes tasques són opcionals, pots fer-les o no.
These assignments are optional, you can do them or not.
Here, 'opcional' is used to specify that it is not required to bring a backpack, emphasizing the choice involved.