This is the 3rd most frequent Portuguese word.
que
"Que" means "that," "what," or "which," depending on context.
Emphasizes an exclamation or exclamatory statement.
Que dia maravilhoso!
What a wonderful day!
Introduces a subordinate clause conveying additional information.
Eu sei que ele virá.
I know that he will come.
Refers to a relative pronoun introducing a dependent clause describing the preceding noun, acting as a descriptor.