This is the 130th most frequent Greek word.
αεκ
"ΑΕΚ" is an acronym for "Athlitiki Enosi Konstantinopouleos," meaning "Athletic Union of Constantinople," a Greek sports club.
In this sentence, 'ΑΕΚ' is used as a proper noun, referring to the sports team AEK.
Η ΑΕΚ κέρδισε τον αγώνα χτες.
AEK won the match yesterday.
Here, 'ΑΕΚ' again refers to the team, but in the context of fandom and personal preference.
Ο φίλος μου είναι μεγάλος οπαδός της ΑΕΚ.
My friend is a big fan of AEK.
'ΑΕΚ' is used in the context of its historical and cultural significance here.