In Portuguese, what does "O" in "O que" literally mean?

Answer 1

“O que”:

"O" is a 'pronome expletivo.' It has only the highlight function

“Que” is an indefinite pronoun; synonymous with  “qual coisa=what thing.” It is used in direct and indirect questions, it is also called the interrogative pronoun.

In the construction “O que,” the pronoun "que" that comes with the 'pronome expletivo' "o":

O que significa isso? (What does it mean?)

O que aconteceu aqui? (What happened here?)

O que é que é? (What is it?)

In this case, "O" is a 'pronome expletivo' and can be removed from the sentence without changing the meaning:

Que significa isso? (What does it mean?)

Que aconteceu aqui? (What happened here?)

Que é que é? (What is it?)