This is the 480th most frequent Portuguese word.
alguém
Someone.
'Alguém' is an indefinite pronoun used here to indicate an unspecified person.
Alguém bateu na porta.
Someone knocked on the door.
'Alguém' is specifically used as the object of the verb 'ouvir', again referring to an unidentified individual.
Eu ouvi alguém chamando meu nome.
I heard someone calling my name.
'Alguém' is used here in an interrogative context, seeking information about an unspecified but potentially existing person.