What do the seven seals in the Bible mean?

In chapters 6 (beginning with verse 1) to 8 (up to and including verse 2) of Revelation, John describes the vision of a Lamb (Jesus) opening seven seals on a book. The following is a brief overview of the 7 seals and their associated events.

The 1st seal

Rider on a white horse
This is the antichrist
Revelation 6:1-2

The 2nd seal

Rider on a red horse
Bloodshed on Earth through wars
Revelation 6:3-4

The 3rd seal

Rider on a black horse
Famine on the earth
Revelation 6:5-6

The 4th seal

Pale horse
One quarter of humanity dies as a result of wars, famines and “by the wild beasts of the earth.” (NIV) — Think of the already occurring swine flu, mad cow disease, bird flu)
Revelation 6:7-8

The 5th seal

Souls under the altar
Those people who were slaughtered because they believed in Jesus
Revelation 6:9-11

The 6th seal

Natural disasters
The people are completely distressed and hide in caves
Revelation 6:12-17

The 7th seal

When the seventh seal of Jesus is opened, “there was silence in heaven for about half an hour.” (NIV)
Revelation 8:1

After that, seven angels standing before God receive seven trumpets. Now God’s further judgment is being carried out on a disobedient and rebellious humanity, which has turned to the dark realm of the devil.