Again; once more — an adverb used when something happens repeatedly, often with a tone of surprise or mild annoyance.
またまた冗談でしょ？
Oh come on, you're joking again, right?
彼はまたまた遅刻した。
He was late again.
会議でまたまた同じ問題が出た。
The same issue came up again in the meeting.
「またまたそんなことを言って！」と母はあきれた。
"Not that again!" said my mother in exasperation.