What does the bible say ...
A final 7 year period of time in which mankind will make a choice as to where they will spend eternity ... Heaven or Hell. They will follow the god of this world (satan) or Jesus the Christ, creator of the universe.
What is the Tribulation? - How do we know the Tribulation will last seven years?
An understanding of Daniel 9:24-27 is necessary in order to understand the purpose and time of the tribulation. This passage speaks of 70 weeks that have been declared against “your people.” Daniel's people are the Jews, the nation of Israel, and Daniel 9:24 speaks of a period of time that God has given “to finish transgression, to put an end to sin, to atone for wickedness, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy.” God declares that “seventy sevens” will fulfill all these things. This is 70 sevens of years, or 490 years. (Some translations refer to 70 weeks of years.) This is confirmed by another part of this passage in Daniel. In verses 25 and 26, Daniel is told that the Messiah will be cut off after “seven sevens and sixty-two sevens” (69 total), beginning with the decree to rebuild Jerusalem. In other words, 69 sevens of years (483 years) after the decree to rebuild Jerusalem, the Messiah will be cut off. Biblical historians confirm that 483 years passed from the time of the decree to rebuild Jerusalem to the time when Jesus was crucified. Most Christian scholars, regardless of their view of eschatology (future things/events), have the above understanding of Daniel's 70 sevens.
With 483 years having passed from the decree to rebuild Jerusalem to the cutting off of the Messiah, this leaves one seven-year period to be fulfilled in terms of Daniel 9:24: “to finish transgression, to put an end to sin, to atone for wickedness, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy.” This final seven-year period is known as the tribulation period—it is a time when God finishes judging Israel for its sin.
Daniel 9:27 gives a few highlights of the seven-year tribulation period: “He will confirm a covenant with many for one 'seven.' In the middle of the 'seven' he will put an end to sacrifice and offering. And on a wing of the temple he will set up an abomination that causes desolation, until the end that is decreed is poured out on him.” The person of whom this verse speaks is the person Jesus calls the “abomination that causes desolation” (Matthew 24:15) and is called “the beast” in Revelation 13. Daniel 9:27 says that the beast will make a covenant for seven years, but in the middle of this week (3 1/2 years into the tribulation), he will break the covenant, putting a stop to sacrifice. Revelation 13 explains that the beast will place an image of himself in the temple and require the world to worship him. Revelation 13:5 says that this will go on for 42 months, which is 3 1/2 years. Since Daniel 9:27 says that this will happen in the middle of the week, and Revelation 13:5 says that the beast will do this for a period of 42 months, it is easy to see that the total length of time is 84 months or seven years. Also see Daniel 7:25, where the “time, times, and half a time” (time=1 year; times=2 years; half a time=1/2 year; total of 3 1/2 years) also refers to “great tribulation,” the last half of the seven-year tribulation period when the beast will be in power.
For further references about the tribulation, see Revelation 11:2-3, which speaks of 1260 days and 42 months, and Daniel 12:11-12, which speaks of 1290 days and 1335 days. These days have a reference to the midpoint of the tribulation. The additional days in Daniel 12 may include the time at the end for the judgment of the nations (Matthew 25:31-46) and time for the setting up of Christ's millennial kingdom (Revelation 20:4-6).
In summary, the Tribulation is the 7-year time period in the end times in which humanity's decadence and depravity will reach its fullness, with God judging accordingly.
You need to make sure your a tribulation saint ...
eternity (heaven or Hell) is a long time to be wrong.
What are tribulation saints
The tribulation will be a time of great trouble for the wicked, because of God’s judgments. It will also be a time of great persecution for the believers—or saints—because of the Antichrist’s persecution (Revelation 13:7). Daniel saw the Antichrist “waging war against the saints and defeating them” (Daniel 7:21). Of course, the saints’ eternal salvation is secure: Daniel also saw that “the Ancient of Days came and pronounced judgment in favor of the saints of the Most High, and the time came when they possessed the kingdom” (Daniel 7:22; cf.Revelation 14:12–13).
The tribulation saints will hear the gospel from several possible sources. The first is the Bible; there will be many copies of the Bible left in the world, and when God’s judgments begin to fall, many people will likely react by finding a Bible to see if prophecies are being fulfilled. Many of the tribulation saints will also have heard the gospel from the two witnesses (Revelation 11:1–13). The Bible says these two individuals “will prophesy for 1,260 days [three and a half years]” (verse 3) and perform great miracles (verse 6). And then there are the 144,000 Jewish missionaries who are redeemed and sealed by God during the tribulation (Revelation 7:1–8). Immediately following the description of their sealing in Revelation 7, we read of the multitudes of tribulation saints who are saved from every corner of the world (verses 9–17).
The tribulation saints will serve their Lord Jesus Christ in the midst of desperate surroundings. Faithful to the end, many of these believers will die for their faith. But in their death, they overcome; “They overcame [Satan] by the blood of the Lamb and by the word of their testimony; they did not love their lives so much as to shrink from death” (Revelation 12:11). And God will reward them: “He who sits on the throne will spread his tent over them. Never again will they hunger; never again will they thirst. The sun will not beat upon them, nor any scorching heat. For the Lamb at the center of the throne will be their shepherd; he will lead them to springs of living water. And God will wipe away every tear from their eyes” (Revelation 7:15–17).
We praise the Lord that the great day of trouble will also be a great day of grace. Even as God is meting out His just punishment on an unbelieving world, He will be restoring Israel to faith and extending grace to all who believe, both Jew and Gentile. God has always been in the business of saving people, and that salvation will still be available during the tribulation. Don’t wait any longer, receive Jesus now (John 1:12).