There is consistency in the Old Testament when it comes to certain Endtimes related phrases. Sometimes they are used generally while other instances are more like very specific Technical Terms.

The Day of the Lord

The Day of the Lord is a technical term referring to major times of Judgement from God. It is used quite often to refer to the Tribulation period.

Earliest usage: Amos 5:18 – “Alas, you who are longing for the day of the Lord, For what purpose will the day of the Lord be to you? It will be darkness and not light;”

Ezekiel 13:5 – O Israel, your prophets have been like foxes among ruins. 5 “You have not gone up into the breaches, nor did you build the wall around the house of Israel to stand in the battle on the day of the Lord.

Joel 2:1 – And sound an alarm on My holy mountain! Let all the inhabitants of the land tremble, For the day of the Lord is coming; Surely it is near, A day of darkness and gloom. A day of clouds and thick darkness. As the dawn is spread over the mountains, So there is a great and mighty people; There has never been anything like it, Nor will there be again after it To the years of many generations….  The sun and the moon grow dark, And the stars lose their brightness. And the Lord utters His voice before His army; Surely His camp is very great, For strong is he who carries out His word. The day of the Lord is indeed great and very awesome, And who can endure it?

Zephaniah 1:18 – 18 Neither their silver nor their gold Will be able to deliver them On the day of the Lord’s wrath; And all the earth will be devoured In the fire of His jealousy, For He will make a complete end, Indeed a terrifying one, Of all the inhabitants of the earth.

Joel 2:31 – The sun will be turned into darkness, And the moon into blood, Before the great and awesome day of the Lord comes. 3:13 – Put in the sickle, for the harvest is ripe. Come, tread, for the wine press is full; The vats overflow, for their wickedness is great. Multitudes, multitudes in the valley of decision! For the day of the Lord is near in the valley of decision. The sun and moon grow dark, And the stars lose their brightness. 16 And the Lord roars from Zion And utters His voice from Jerusalem, And the heavens and the earth tremble.

Verified in the NT

1 Thess. 2:1 – Now we request you, brethren, with regard to the coming of our Lord Jesus Christ, and our gathering together to Him, that you may not be quickly shaken from your composure or be disturbed either by a spirit or a message or a letter as if from us, to the effect that the day of the Lord has come. Let no one in any way deceive you, for it will not come unless the apostasy comes first, and the man of lawlessness is revealed, the son of destruction, who opposes and exalts himself above every so-called god or object of worship, so that he takes his seat in the temple of God, displaying himself as being God.

1 Thess. 5:1 – Now as to the times and the epochs, brethren, you have no need of anything to be written to you. For you yourselves know full well that the day of the Lord will come just like a thief in the night. While they are saying, “Peace and safety!” then destruction will come upon them suddenly like birth pangs upon a woman with child; and they shall not escape.

2 Peter 3:10 – But the day of the Lord will come like a thief, in which the heavens will pass away with a roar and the elements will be destroyed with intense heat, and the earth and its works will be burned up.

The Time of Jacobs trouble

Jer 30:7 – The word that came to Jeremiah from the LORD, saying, Thus speaketh the LORD God of Israel, saying, Write thee all the words that I have spoken unto thee in a book. For, lo, the days come, saith the LORD, that I will bring again the captivity of my people Israel and Judah, saith the LORD: and I will cause them to return to the land that I gave to their fathers, and they shall possess it. And these are the words that the LORD spake concerning Israel and concerning Judah. For thus saith the LORD; We have heard a voice of trembling, of fear, and not of peace. Ask ye now, and see whether a man doth travail with child? wherefore do I see every man with his hands on his loins, as a woman in travail, and all faces are turned into paleness? Alas! for that day is great, so that none is like it: it is even the time of Jacob’s trouble; but he shall be saved out of it.

The Last Days

Isaiah 2:2 – The millennial kingdom – Now it will come about that In the last days, The mountain of the house of the Lord Will be established as the chief of the mountains, And will be raised above the hills; And all the nations will stream to it.And many peoples will come and say, “Come, let us go up to the mountain of the Lord, 3 To the house of the God of Jacob; That He may teach us concerning His ways, And that we may walk in His paths.

Acts 2:17 – Quoting Joel 2:28 – And it shall be in the last days,’ God says, ‘That I will pour forth of My Spirit upon all mankind; Here Peter claims we are in the last days.

Hebrews 1:1 – God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, in these last days has spoken to us in His Son

The term last days is referred to in different senses defined by the context;  

The Day of Reckoning (Day of the Lord)

Isaiah 2:12 – For the Lord of hosts will have a day of reckoning Against everyone who is proud and lofty, And against everyone who is lifted up, That he may be abased.

In That Day

Zechariah

12:1-4 – “In that day,” declares the LORD, “I will strike every horse with bewilderment and his rider with madness. But I will watch over the house of Judah, while I strike every horse of the peoples with blindness. ⁵“Then the clans of Judah will say in their hearts, ‘A strong support for us are the inhabitants of Jerusalem through the LORD of hosts, their God.’

14:4 – And in that day His feet will stand on the Mount of Olives, which is in front of Jerusalem on the east; and the Mount of Olives will be split in its middle from east to west by a very large valley, so that half of the mountain will move toward the north and the other half toward the south

Joel 3:18 – And it will come about in that day That the mountains will drip with sweet wine, And the hills will flow with milk, And all the brooks of Judah will flow with water; And a spring will go out from the house of the Lord,

The context of the passage will determine its usage.

Abomination of Desolation

Somewhat different from the above, this refers to the Antichrist, and what he will do at the midpoint of the Tribulation period —  stopping the temple daily sacrifice, and setting himself up as God — that is the abomination. The temple sacrifice is an interesting prophecy considering that the Jews don’t have a temple or sacrifices. They will.

Daniel 11:29 – At the appointed time he will return and come into the South, but this last time it will not turn out the way it did before.  “For ships of Kittim will come against him; therefore he will be disheartened, and will return and become enraged at the holy covenant and take action; so he will come back and show regard for those who forsake the holy covenant.  “And forces from him will arise, desecrate the sanctuary fortress, and do away with the regular sacrifice. And they will set up the abomination of desolation.

Daniel 12:9 – “Go your way, Daniel, for these words are concealed and sealed up until the end time. “Many will be purged, purified and refined; but the wicked will act wickedly, and none of the wicked will understand, but those who have insight will understand. “And from the time that the regular sacrifice is abolished, and the abomination of desolation is set up, there will be 1,290 days. (Using the 30-day month, 3.5 years = 1260 days – Midpoint of the Tribulation) 

Matthew 24:15 – “Therefore when you see the abomination of desolation which was spoken of through Daniel the prophet, standing in the holy place (let the reader understand), 16 then let those who are in Judea flee to the mountains;  let him who is on the housetop not go down to get the things out that are in his house; and let him who is in the field not turn back to get his cloak. This refers to the Nation of Israel and the Holy City of Jerusalem.