This is the 3832nd most frequent French word.
youssef
"Youssef" is not a French word but a masculine given name, equivalent to "Joseph" in English.
In this sentence, 'Youssef' is used as a proper noun representing someone's name.
Youssef est un excellent joueur de football.
Youssef is an excellent football player.
Here, 'Youssef' functions as the direct object of the verb, indicating the person to whom an action was directed.
J'ai prêté mon livre à Youssef hier.
I lent my book to Youssef yesterday.
In this context, 'Youssef' is referred to indirectly, being the subject of the discussion indicated in the sentence.