This is the 6th most frequent Romanian word.
că
"That" (used to introduce a subordinate clause).
In this sentence, 'că' is used as a conjunction introducing a subordinate clause that specifies content.
Cred că mâine va ploua.
I think that it will rain tomorrow.
Here, 'că' serves as a conjunction linking the main clause to the reported statement.
El spune că este fericit.
He says that he is happy.
In this example, 'că' introduces a subordinate clause conveying information related to the main question.