'Great Tribulation' in the Bible

for then will be great tribulation, such as has not happened from the beginning of the world until now; no, nor ever shall be.

"Now there came a famine upon the whole of Egypt and Canaan, and great tribulation; and our fathers were not finding sustenance.

Behold, I cast her into a bed, and those committing adultery with her, into great tribulation, if they repent not of their works.

And I have said to him, "My lord, you know." And he said to me, "These are those who come out of the great tribulation; and they washed their robes, and made them white in the blood of the Lamb.