This is the 4939th most frequent Turkish word.
futbolu
"Futbolu" means "the football" or "the soccer" in English, referring to the sport in the accusative case in Turkish.
Here, 'futbolu' is the accusative form of 'futbol', used because 'sever' (likes) is a transitive verb that requires its direct object in the accusative form.
Kardeşim futbolu çok sever.
My sibling likes football very much.
In this sentence, 'futbolu' is also in the accusative form, used as the direct object of the verb 'oynarız' (we play).
Biz her yaz tatilinde genellikle futbolu oynarız.
We usually play football during every summer vacation.
Here, 'futbolu' is the accusative form indicating the object of the infinitive 'öğrenmek' (to learn).