What does "the day of the Lord" mean?

Nothing, in reality.

The biblical text in Joel 2:31, suggests an eclipse does not the moon, but the planet Venus in its transit by the Earth.

● Joel 2:31 » The sun shall be turned into darkness, and the moon into blood, before the great and terrible day of Jehovah cometh.

Is Venus Nibiru??? (Venus = Eden = Nibiru = Planet-X)

The landscape below is a conception of how will be the coming of the Lord Jesus Christ (the Son of Man) to Earth.

● Matthew 24:27 » For as the lightning cometh forth from the east, and is seen even unto the west; so shall be the coming of the Son of man.

● Matthew 24:30 » and then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming on the clouds of heaven with power and great glory.

● Matthew 24:31 » And he shall send forth his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.

● Revelation 22:16 » I Jesus have sent mine angel to testify unto you these things for the churches. I am the root and the offspring of David, the bright, the morning star.

The landscape

http://odemori.blogspot.com/2011/01/is-venus-nibir...

I believe that the day of the Lord refers to the end of this present age when Jesus returns to set up his Father's kingdom. We have a time of great trouble as we see in Zechariah 14 when Jesus returns, in the name of his Father, to intervene in the warfare that has reached a terrible point. It is all a conclusion to the time when men's hearts are failing them for fear of the things coming on the earth.

We can at present see what look to be signs of these things starting to happen. The Middle East seems to be in a ferment with people sickened by the dictators who have exercised an evil type of control over their countrymen and women. I heard the other day on the radio of people in Egypt, who before the present more democratic system, used to walk past the police stations on the other side of the road because of the horror of the screams from torture they heard from within.

We are told to Watch for this day of the coming of the Lord Jesus in the glory of his Father will come when we least expect it. The sign given by Jesus was of that of Noah when men were marrying and being given in marriage until the flood came and swept them all away. In other words they were getting on with their lives without giving the LORD God a thought.

The phrase “day of the Lord” usually identifies events that take place at the end of history (Isaiah 7:18-25) and is often closely associated with the phrase “that day.” One key to understanding these phrases is to note that they always identify a span of time during which God personally intervenes in history, directly or indirectly, to accomplish some specific aspect of His plan.

Most people associate the day of the Lord with a period of time or a special day that will occur when God’s will and purpose for His world and for mankind will be fulfilled. Some scholars believe that the day of the Lord will be a longer period of time than a single day—a period of time when Christ will reign throughout the world before He cleanses heaven and earth in preparation for the eternal state of all mankind. Other scholars believe the day of the Lord will be an instantaneous event when Christ returns to earth to redeem His faithful believers and send unbelievers to eternal damnation.

The phrase “the day of the Lord” is used nineteen times in the Old Testament (Isaiah 2:12; 13:6, 9; Ezekiel 13:5, 30:3; Joel 1:15, 2:1,11,31; 3:14; Amos 5:18,20; Obadiah 15; Zephaniah 1:7,14; Zechariah 14:1; Malachi. 4:5) and four times in the New Testament (Acts 2:20; 2 Thessalonians 2:2; 2 Peter 3:10). It is also alluded to in other passages (Revelation 6:17; 16:14).

The Old Testament passages dealing with the day of the Lord often convey a sense of imminence, nearness, and expectation: “Wail, for the day of the Lord is near!” (Isaiah 13:6); “For the day is near, even the day of the Lord is near” (Ezekiel 30:3); “Let all who live in the land tremble, for the day of the Lord is coming. It is close at hand” (Joel 2:1); “Multitudes, multitudes in the valley of decision! For the day of the Lord is near in the valley of decision” (Joel 3:14); “Be silent before the Lord God! For the day of the Lord is near” (Zephaniah 1:7). This is because the Old Testament passages referring to the day of the Lord often speak of both a near and a far fulfillment, as does much of Old Testament prophecy. Some Old Testament passages that refer to the day of the Lord describe historical judgments that have already been fulfilled in some sense (Isaiah 13:6-22; Ezekiel 30:2-19; Joel 1:15, 3:14; Amos 5:18-20; Zephaniah 1:14-18), while others refers to divine judgments that will take place toward the end of the age (Joel 2:30-32; Zechariah 14:1; Malachi 4:1, 5).

The New Testament calls it a day of “wrath,” a day of “visitation,” and the “great day of God Almighty” (Revelation 16:14) and refers to a still future fulfillment when God’s wrath is poured out on unbelieving Israel (Isaiah 22; Jeremiah 30:1-17; Joel 1-2; Amos 5; Zephaniah 1) and on the unbelieving world (Ezekiel 38–39; Zechariah 14). The Scriptures indicate that “the day of the Lord” will come quickly, like a thief in the night (Zephaniah 1:14-15; 2 Thessalonians 2:2), and therefore Christians must be watchful and ready for the coming of Christ at any moment.

Besides being a time of judgment, it will also be a time of salvation as God will deliver the remnant of Israel, fulfilling His promise that “all of Israel will be saved” (Romans 11:26), forgiving their sins and restoring His chosen people to the land He promised to Abraham (Isaiah 10:27; Jeremiah 30:19-31, 40; Micah 4; Zechariah 13). The final outcome of the day of the Lord will be that “the arrogance of man will be brought low and the pride of men humbled; the Lord alone will be exalted in that day” (Isaiah 2:17). The ultimate or final fulfillment of the prophecies concerning the day of the Lord will come at the end of history when God, with wondrous power, will punish evil and fulfill all His promises.

It usually refer to a period of time in which God is directly involved in human affairs through either judgment or blessing. These quotes mostly refer to the last judgment.

The last day

The Second Coming of Christ.