The basics: Egypt is a large, mostly Arab, mostly Muslim country. At around 80 million people, it has the largest population in the Middle East and the third-largest in Africa. Most of Egypt is in North Africa, although the part of the country that borders Israel, the Sinai peninsula, is in Asia. Its other neighbors are Sudan (to the South), Libya (to the West), and Saudi Arabia (across the Gulf of Aqaba to the East). It has been ruled by Hosni Mubarak since 1981.
What's happening? Inspired by the recent protests that led to the fall of the Tunisian government and the ousting of longtime Tunisian dictator Zine El Abidine Ben Ali, Egyptians have joined other protesters across the Arab world (in Algeria, notably) in protesting their autocratic governments, high levels of corruption, and grinding poverty. In Egypt, tens of thousands of protesters have taken to the streets. Here's a photo of one of the protests in Cairo, the capital (via Twitter):
Why are Egyptians unhappy? They have basically no more freedom than Tunisians. Egypt is ranked 138th of 167 countries on The Economist's Democracy index, a widely accepted measure of political freedom. That ranking puts Egypt just seven spots ahead of Tunisia. And Egyptians are significantly poorer than their cousins to the west.
How did this all start? This particular round of protests started with the protests in Tunisia. But like their Tunisian counterparts, Egyptian protesters have pointed to a specific incident as inspiration for the unrest. Many have cited the June 2010 beating death of Khaled Said (warning: graphic photos), allegedly at the hands of police, as motivation for their rage. But it's also clear that the issues here are larger.
Why is this more complicated for the US than Tunisia was? The Tunisian regime was a key ally for the US in the fight against Al Qaeda. But the US government's ties to Tunisia's Ben Ali pale in comparison to American ties to Egypt. Shadi Hamid of the Brookings Institution, a centrist think tank, explains:
Predictions that a Tunisia-like uprising will soon topple Egyptian President Hosni Mubarak are premature—the Egyptian regime, with its well-paid military, is likely to be more unified and more ruthless than its Tunisian counterparts were... The U.S. is the primary benefactor of the Egyptian regime, which, in turn, has reliably supported American regional priorities. After Iraq, Afghanistan, and Israel, Egypt is the largest recipient of U.S. assistance, including $1.3 billion in annual military aid. In other words, if the army ever decides to shoot into a crowd of unarmed protestors, it will be shooting with hardware provided by the United States. As Steven Cook of the Council on Foreign Relations points out, the Egyptian military is "not there to project power, but to protect the regime."