Jeremiah prophesied that Israel would be conquered by Babylon and remain in captivity for seventy years.

This whole country will become a desolate wasteland, and these nations will serve the king of Babylon seventy years. Jer 25:11

At the end of that 70 years of captivity, Daniel, being aware of this prophecy (Daniel 9:2-3), prayed and fasted on behalf of his people Israel. 

O my God, incline Your ear and hear! Open Your eyes and see our desolations and the city which is called by Your name; for we are not presenting our supplications before You on account of any merits of our own, but on account of Your great compassion. O Lord, hear! O Lord, forgive! O Lord, listen and take action! For Your own sake, O my God, do not delay, because Your city and Your people are called by Your name. Dan 9:18-19

While Daniel was praying, the archangel Gabriel came to Daniel and revealed to him the "70 weeks prophecy".

Seventy weeks are decreed for your people and your holy city to stop their transgression, to put an end to sin, to make atonement for iniquity, to bring in everlasting righteousness, to seal up vision and prophecy, and to anoint the Most Holy Place. Dan 9:24

The word "weeks" comes from the Hebrew word "shabua" - which literally means seven. Some translations properly word this statement from Gabriel as "Seventy sevens are decreed for your people...". Gabriel continues...

Know and understand this: From the time the word goes out to restore and rebuild Jerusalem until the Anointed One, the ruler, comes, there will be seven sevens, and sixty-two sevens. Dan 9:25

There are two partitions here. Seven sevens correspond to "restoring and rebuilding Jerusalem" and then the next sixty-two sevens correspond to the "Anointed One" or ruler that comes. These "sevens" are blocks of "seven years". This is not unusual. The same methodology is used in the Bible to calculate Jubilee years (Lev 25:8). So...

  • the first seven sevens = 49 years to restore and rebuild Jerusalem
  • seven sevens + the sixty-two sevens = 483 years until the Annointed one comes.

It is believed that the decree to rebuild Jerusalem was issued in 457 BC. Adding 483 years to this date, we arrive at 27AD - believed to be the time that Christ began his ministry. Note that there are some discrepancies in the way scholars calculate these dates based on available historical records.

Carrying on with the statement from Gabriel...

After the sixty-two sevens, the Anointed One will be put to death and will have nothing. Dan 9:26a

This is a clear reference to the crucifiction of the Messiah. This occurs after the seven sevens and sixty-two sevens. Gabriel continues...

The people of the ruler who will come will destroy the city and the sanctuary. Dan 9:26b

This is a reference to the destruction of Jerusalem and the temple in 70AD. Continuing on...

The end will come like a flood: War will continue until the end, and desolations have been decreed. Dan 9:26c

So, putting Daniel 9:26 together: the Annointed One is put to death, the city and temple are destroyed, and war and desolations continue to the end. All of this happens after sixty-nine sevens but before the final seven. Gabriel continues...

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 at the temple he will set up an abomination that causes desolation, until the end that is decreed is poured out on him. Dan 9:27

Who is this "He" that confirms a covenant with many for one seven? This person will set up an "abomination that causes desolation" in the temple. This person is referenced by Daniel two more times in this book - Dan 11:31, and Dan 12:11. Jesus himself references this person that brings about the "abonmination that causes desolation" in Matt 24.

So when you see standing in the holy place ‘the abomination of desolation,’ described by the prophet Daniel, then let those who are in Judea flee to the mountains. Matt 24:15-16

Jesus later in the same dialogue describes a period of "great distress, unequaled from the beginning of the world until now" that is triggered by this event. This period, which begins in the middle of this last "seven" is sometimes referred to as the "great tribulation" or the period of "Jacob's trouble". Much of the Book of Revelation details the events during this intense period.

Gabriel's final statement to Daniel regarding this figure is...

"the end that is decreed is poured out on him. "  Dan 9:27

This figure is believed to be the "Antichrist" or "man of lawlessness" that will appear at the end of the age. And Gabriel's final statement is a reference to his final destruction - laid out in Rev 19:11-20. 

So, this final "seven" years is triggered by a "covenant with many".  It should be obvious that Israel and Jerusalem are at the center of this covenant - "Seventy weeks are decreed for your people and your holy city". Whether valid or not, some refer to this final seven year period as the "tribulation". Though it is clear that by the mid-point of this seven, after the abomination that causes desolation, "great tribulation" does break out "until the end that is decreed" or judgement is poured out.