Alas for that day! For the day of the LORD is near; it will come like destruction from the Almighty. Joel 1:15

Woe to you who long for the day of the LORD! Why do you long for the day of the LORD? That day will be darkness, not light.  Amos 5:18

The day of the LORD is near for all nations. As you have done, it will be done to you; your deeds will return upon your own head. Obadiah 1:15

See, I will send the prophet Elijah to you before that great and dreadful day of the LORD comes. Malachi 4:5

The sun will be turned to darkness and the moon to blood before the coming of the great and glorious day of the Lord. Acts 2:20

for you know very well that the day of the Lord will come like a thief in the night... 1 Thessalonians 5:2

But the day of the Lord will come like a thief. The heavens will disappear with a roar; the elements will be destroyed by fire, and the earth and everything done in it will be laid bare.  2 Peter 3:10

The pharse means "the day the Lord is victorious."  It is a term of judgment, carried out by the Lord who uses invading armies to carry out his sentence.

This phrase "day of the Lord" appears 18 times in the Old Testament.  When used, it pointed to the day when the Lord would punish Israel and Judah for their sins.  For Israel that occurred in 740-732 BC when Assyria invaded the Northern Kingdom.  For Judah that occurred in 588 BC when Babylon invaded Jerusalem.

In the New Testament use of "the day of the Lord" points to one of two events: the destruction of Jerusalem in 70 AD by Roman armies or the day when the Lord ends the earth, resurrects the dead, judges their souls and reigns over a new heaven and new earth.

It is not a good term and means death and destruction for someone, except for Christians on the final day of judgment.  Every time, God showed patience and gave warning, but when things just would not change, he had to allow for the destruction.  On that day, God showed once again that he was right and we were wrong.