In preparation for Debate Night I'm going to be writing two diaries. This one covers what the Electoral College is exactly, while the other is a statement of position.

ORIGINS

The original source of the EC is the Constitution, specifically Article 2 section 1 subsection 3:

The Electors shall meet in their respective States, and vote by Ballot for two persons, of whom one at least shall not lie an Inhabitant of the same State with themselves. And they shall make a List of all the Persons voted for, and of the Number of Votes for each; which List they shall sign and certify, and transmit sealed to the Seat of the Government of the United States, directed to the President of the Senate. The President of the Senate shall, in the Presence of the Senate and House of Representatives, open all the Certificates, and the Votes shall then be counted. The Person having the greatest Number of Votes shall be the President, if such Number be a Majority of the whole Number of Electors appointed; and if there be more than one who have such Majority, and have an equal Number of Votes, then the House of Representatives shall immediately chuse by Ballot one of them for President; and if no Person have a Majority, then from the five highest on the List the said House shall in like Manner chuse the President. But in chusing the President, the Votes shall be taken by States, the Representation from each State having one Vote; a quorum for this Purpose shall consist of a Member or Members from two-thirds of the States, and a Majority of all the States shall be necessary to a Choice. In every Case, after the Choice of the President, the Person having the greatest Number of Votes of the Electors shall be the Vice President. But if there should remain two or more who have equal Votes, the Senate shall chuse from them by Ballot the Vice-President.

However the 12th Amendment to the Constitution has changed the way the electors select the president substantially:

The Electors shall meet in their respective states, and vote by ballot for President and Vice-President, one of whom, at least, shall not be an inhabitant of the same state with themselves; they shall name in their ballots the person voted for as President, and in distinct ballots the person voted for as Vice-President, and they shall make distinct lists of all persons voted for as President, and of all voted for as Vice-President, and of the number of votes for each, which lists they shall sign and certify, and transmit sealed to the seat of the government of the United States, directed to the President of the Senate
The President of the Senate shall, in the presence of the Senate and House of Representatives, open all the certificates and the votes shall then be counted;

The person having the greatest number of votes for President, shall be the President, if such number be a majority of the whole number of Electors appointed; and if no person have such majority, then from the persons having the highest numbers not exceeding three on the list of those voted for as President, the House of Representatives shall choose immediately, by ballot, the President. But in choosing the President, the votes shall be taken by states, the representation from each state having one vote; a quorum for this purpose shall consist of a member or members from two-thirds of the states, and a majority of all the states shall be necessary to a choice. And if the House of Representatives shall not choose a President whenever the right of choice shall devolve upon them, before the fourth day of March next following, then the Vice-President shall act as the President, as in the case of the death or other constitutional disability of the President.

The person having the greatest number of votes as Vice-President, shall be the Vice-President, if such number be a majority of the whole number of Electors appointed, and if no person have a majority, then from the two highest numbers on the list, the Senate shall choose the Vice-President; a quorum for the purpose shall consist of two-thirds of the whole number of Senators, and a majority of the whole number shall be necessary to a choice. But no person constitutionally ineligible to the office of President shall be eligible to that of Vice-President of the United States.

So originally the electors voted twice. The person with the most votes became president. The person with the second most votes became Vice President. This naturally led to situations where people of opposed political parties occupied the top two executive seats. The Twelfth Amendment changed things to the more modern version where you have individuals specifically running to be president and others specifically running to be Vice President.

It is worth noting though that neither the Constitution nor the 12th Amendment actually uses the term "Electoral College." They refer instead merely to "Electors."

The exact term "Electoral College" does show up in election law, i.e. here.

Practical Effect

Come election day people do not vote for the president, nor the vice president. They do vote for Senators, Representatives, local government, and on city, county, and state measures.

When a voter seems to vote for a presidential nominee what they are actually doing is voting for a slate of Electors, provided by the nominees party, who promise to then vote for that nominee. It is that second vote, the one placed only by Electors that matters in selecting a president, the popular vote has no bearing on the matter whatsoever, as can be seen by the rare but occasional instances where a candidate has won the presidency while losing the popular vote (or more realistically while their Electors recieved fewer votes nationwide than their opponent's Electors).

Electors for each state are currently awarded entirely to the winner of that state's popular vote. More precisely, which ever party won the popular vote gets their entire slate of Electors, any losing parties get none. This means that getting 49.9% of the vote in a state gets a presidential nominee nothing and getting 50.1% of the vote gets them everything.

The number of Electors for a state is the sum of the number of Senators and the number of Representatives. This means heavily populated states have more Electors than small states but small states are disproportionately represented because every state has two Senators. For example California has 55 Electors and a population of 36.5 million, or 1 Elector for every 663,000 people. Wyoming has 3 Electoral votes and a population of 500,000, or one Elector for every 166,000 people. A Wyoming voter counts more than 3x as much as a california voter, but only if he votes in the majority (for their state).

There are currently 538 Electors (435 for the Representatives, 100 for the Senators, plus 3 special Electors for the District of Columbia) meaning that a presidential nominee requires a minimum of 270 (a simple majority) in order to win. If no candidate gains a majority the matter moves into congress with the House selecting the President and the Senate selecting the Vice President (who would not have to be from the same party, I believe).

California has the most Electoral votes (55), followed by Texas (34) and New York (31). Florida, Illinois, Pennsylvania, and Ohio all have 20 or more EVs. All other states are lower. Seven states and the District of Columbia have the minimum of 3 EVs. A candidates could win with the 11 most populous states (a total of 271 Evs). This would represent 22% of the states but 56% of the population. On the other hand a candidate could also win by winning the 40 least populous states (a total of 282 EVs). This would represent 80% of the states but only 46.5% of the population.

Okay, so that's what the EC is, now we can talkabout what or whether it should be...