What is the electoral college?

The voters cast ballots as symbols of their preference of candidates.  But this has only the suggestion of the final result.
Each state has "electors".  Their number is 538.  100 are for the 100 senators.  438 are for the representatives in the House.  More than half (270 or greater) are needed to "elect" a president and a vice president.  The electors are "pledged" to follow the wishes of the voters in their states.  In most times in history, each of electors have followed the pledge.  But must they?
The electors of the "Electoral College" (not a real college but an assembly) meet in December to finalize the result of the November election.
48 of the 50 states and DC are "winner take all", where the majority of voters put all their electors into the "bucket" for a candidate.  In two states, the electors could be divided among or between candidates.
There are many ways each of this years candidates could win or lose.  State elector totals could swing by a single vote out of millions.  A really close race in any state might mean recounts (remember Florida in 2000?) and court hearings, delaying official results for quite a while.  One candidate has already labeled this election possibly the most corrupt in history.  And he has not said he will have a peaceful transition to another president in January if he loses.
There could even be a tie, 269 to 269.  Then the decision is in the Senate.  Since it is dominated by Republicans now, guess what will happen.  And the unusual part is that if Democrats win enough Senate seats, the new Senate next year and for at least until January 2023 might be controlled by them, as well as the House.  With tRump still in White House, wouldn't he be in a bad way?  The government might come to a complete stop.  Or tRump might use a military take-over of the whole country and run it the way he wants.

It goes back to the early days when the states were powerful.  To protect state rights, the Constitution provides for the Senate, 2 senators per state regardless of population.  Another protection was the electoral college.  The people actually vote for their electoral college of that state. There are actually 2 groups, one republican and one democrat.  The voters elect one or the other to vote for the President. If the people vote republican, the republican electoral college is authorized and they vote for the republican candidate.  This is actually done in Washington, a few days after the election.  Now, the number of members of the electoral college for a state is the number of representatives + the number of senators.  That makes the electoral skewed, just like it makes the senate skewed if you consider the popular vote like the House to be some supreme methodology of democracy.  It is just the liberal/democrat point of view to gain an advantage since high population density states tend to be democrat and lower population density states tend to be republican.  Thus, republican states have an advantage because of the number of senators and the older concept of state rights if you consider the popular vote concept to be more fair.  You might also consider what would happen to the USA if California, New York could control the federal government.  It would be the same thing as "packing" the supreme court.  Big trouble would ensue since the minority has no input.  Again, to repeat for those who do not grasp the concept.  It is a way so that the minority states/citizens have a determination of their rights. If you exclude the minority by always doing things the majority way, there will be big problems. Don't underestimate the concept of state rights.  Civil war fought over that issue.

--  As an Australian with a strong interest in politics I have never understood the American Electoral College, even watching the link supplied by "Rick". To me, it is the most undemocratic scheme that makes the US presidential elections undemocratic.

Here is a link.

Starrysky has a lot right, but got some details wrong.  For example, if the electoral college is tied, then the Senate picks the Vice President but the members of the House of Representatives pick the President.  However, it's one vote per state, not per member, so even though over half the House is currently Democrats, Republicans (who control over half the states) would have the advantage.