On 3 November, Americans will head to the polls and send either Joe Biden or Donald Trump to the White House. Here's what to watch for as an unpredictable election night unfolds, and the results roll in. Some key details: To win the US presidency, earning the popular vote is not actually the way to do it. Instead, both candidates are aiming to secure at least 270 of the 538 votes in the electoral college Millions more Americans are voting by mail than in past elections, meaning there will almost certainly be a days-long wait for final results as postal ballots are collected and tallied. And because of this unprecedented surge of mail-in ballots early leaders may not end up winning, so be wary of preliminary results Some key terms: Bellwether state: Places like Ohio and Missouri where voters have proven reliable at choosing the national winner Exit poll: In-person interviews with voters as they leave their polling locations. The numbers we get from exit polls are distinct from actual ballot tallies, which will be used for the final results. Electoral college: A group of electors who meet every four years, a few weeks after election day, to choose the president and vice-president. Projections v calling: On election night, ballot counts will be used to predict - or project - the likely winner of each state and the nationwide vote. A state will not be "called", however, until enough data has been collected to declare a clear winner. That includes months of polling, exit polls on the day and some of the actual votes counted. Swing state or battleground state: These states lack a clear party affiliation, meaning they are up for grabs for both Democratic and Republican candidates. Red state v blue state: These states tend to vote with a particular party - Republicans in red states and Democrats in blue. How to know who's winning The influx of postal ballots this year will make it hard to see who's in the lead early on. Different states have different rules for how - and when - to count postal ballots, meaning there will be large gaps between them in terms of reporting results. Some states, like Florida and Arizona, begin pre-processing ballots weeks before 3 November. Others, like Wisconsin and Pennsylvania, won't touch these votes until election day, meaning they'll likely be slower to count. To add to the confusion, states differ in their deadlines for when to accept postal ballots. Some, like Georgia, will only count ballots received on or before 3 November, while others, like Ohio, will count late ballots as long as they are postmarked by 3 November. We know for certain that in some states it will take weeks to get complete results, meaning it will be nearly impossible to predict when we can officially name the next president. This hasn't been the case in past elections, when you could typically set your watch to the 23:00 EST (04:00 GMT) closure of West Coast polls. In 2008, results came right on the hour and in 2012 they were just 15 minutes after that. The last time around, however, it wasn't until Donald Trump clinched Pennsylvania deep into election night - 01:35 EST (06:35 GMT) - that his victory over Hillary Clinton was considered inevitable.