I've heard that; rumor has it that
Used to convey hearsay or information obtained from another source. Often follows a clause ending in ～らしい, ～そうだ, or a plain form.
明日は雨が降るということだ。
I've heard that it will rain tomorrow.
彼は来月転勤するということだ。
Rumor has it that he will be transferred next month.
it appears that; it seems that
Expresses the speaker's conjecture about another person's feelings, thoughts, or situation, often based on observable signs. Commonly follows a clause ending in ～たい, ～がる, or a plain form describing a state.
彼はとても嬉しそうだ。試験に合格したということだ。
He looks very happy. It appears that he passed the exam.
The fact that she says nothing means she is still angry.
そうだ (hearsay) attaches to the plain form of verbs/adjectives and is more direct; ということだ can be used to rephrase or summarize information, adding a nuance of 'this is what I've heard/understood'.
Combination of the particle と (quotative), the verb 言う (to say), the nominalizer こと, and the copula だ. Literally 'it is that (someone) says...', which developed into a fixed expression for hearsay and conjecture.