A: The word that we usually translate as "tribulation" comes from the Greek "thlipsis," which can mean sorrow, affliction, grief, and even a squeezing (in a way to cause pain and discomfort).
Jesus told his disciples that they would have tribulation because of following him: "In the world you are having tribulation, but take courage! I have conquered the world.” (John 16:33) Many would stumble on account of the tribulation. "As for the one sown upon the rocky places, this is the one hearing the word and at once accepting it with joy. Yet he has no root in himself but continues for a time, and after tribulation or persecution has arisen on account of the word he is at once stumbled." (Matt. 13:20,21) Such tribulation upon Jesus' disciples would especially be severe in the last days. (Matt. 24:9-13; 2 Tim. 3:1)
In 2 Thessalonians 1:6-10 the apostle Paul refers to two distinct "tribulations." In verse 6, he says, "it is righteous on God's part to repay tribulation to those who make tribulation for you." This is the tribulation we are suffering in the world, just as Jesus also suffered. (Matt. 10:17-23; John 15:18-21; 16:1-4) But this tribulation is certainly not the “great tribulation.” According to Paul's letter to the Thessalonians, the great tribulation is what Jesus brings upon those who have been responsible for our tribulation, because "it is righteous on God's part to repay tribulation to those who make tribulation for you," at “the revelation of the Lord Jesus from heaven with his powerful angels in a flaming fire, as he brings vengeance upon those who do not know God and those who do not obey the good news about our Lord Jesus. These very ones will undergo the judicial punishment of everlasting destruction from before the Lord and from the glory of his strength.” (2 Thess. 1:6-10; 1 Cor. 3:17)
The destruction that God executes upon Babylon the Great is in itself not the great tribulation that Jesus spoke of in Matthew 24:21; but it will be quickly followed by the greatest of all tribulations, also known as the day of Jehovah, Armageddon. (Zeph. 1:14-18; Rev. 16:14, 16) Satan's entire political system, which has been in opposition to Jehovah from the beginning, will be totally annihilated and destroyed, along with any "who do not know God and those who do not obey the good news about our Lord Jesus." (Daniel 7:26; Rev. 19:11-21) How will it be determined who it is that did not know God and therefore did not obey the good news about our Lord Jesus? In the days to come Jehovah will maneuver events that will allow everyone to clearly demonstrate and give evidence as to where they stand in connection with the all important issue of his kingdom. (Rev. 3:10)
As you can see, the word "tribulation" refers to two different things in 2 Thessalonians 1:6-8; from the tribulation that we experience at the hands of our opposers, including from some within God's own household, to the greatest of all tribulations “at the revelation of Jesus from heaven with his powerful angels,” at Armageddon.