US Election Vocabulary: Electoral college? Battleground states?

US presidential elections are not decided by the popular vote. Each voter essentially votes for a state representative in an electoral college. States send delegates to this college, the number being decided by the population of the state

Most states are comfortably red (Republican) or blue (Democrat) - see here. This means  that presidential elections are essentially fought over a small number of purple or battleground states which swing between parties in different election cycles.

Ohio is the classic example of a swing state. It has voted for the victor in every election since Kennedy's victory in 1960. Traditional wisdom suggests that the Republicans cannot win without Ohio - the state which decisively swung the re-election of George W Bush in 2004. That is why Governor Romney and President Obama have returned again and again to campaign there.

One curious feature of the electoral college system is that a candidate can win the popular vote but still become president - this was the case in the 2000 election. The distribution of votes is as important as the raw number.