What's NPVIC and what does "census year" mean? european here
The census is when they count all of the people living in the United States (or try to.) This affects how districts are drawn and how many representatives in congress each state has. The president isn't the only person people are voting for in 2020. Electoral votes are determined by the number of representatives a state has plus two (the plus two part is also where some of the electoral college's problems come from, but I'll get to that later.) Basically, the more people the census counts in your state, the more electoral college votes it has, and the more influence your state has over who wins the presidency.
NPVIC stands for "The National Popular Vote Interstate Compact." Basically, it's an agreement states can sign up for that says they'll give all their electoral votes to whomever wins the popular vote instead of the majority in their state specifically. The problem with the electoral college is that a candidate who wins the state by even the tiniest margin gets all of that state's electoral votes. First off, this makes it possible for the candidate most popular with citizens to lose, and it causes candidates to focus on "swing states" with close races over, y'know, the whole goddamn country. That's why there's so much coverage of states no one gives a fuck about like New Hampshire and Iowa during election cycles-- they have really close races, with the voting populous being almost evenly divided between Republican and Democrat. Plus, there's a rule that all states start with two electoral votes before the votes are distributed based on population, which means that states with almost no people on them are "taking" votes from large ones, thereby devaluing the weight of votes cast in populous states. Currently, sixteen states, representing 36% of the electoral votes, have signed NPVIC. However, the compact doesn't go into effect until the states signed on represent at least 50% of the electoral college votes. Currently, fourteen
more states have legislation to join the compact pending. If even only a few of these fourteen join, the compact goes into effect, rendering the electoral college effectively meaningless for choosing a president for the first time in U.S. history.
However, electoral college votes are cast by actual individuals, most of whom have no legal obligation to vote in accordance with their state majority. Voters who go against their state's majority are classed faithless electors, of which there were six in the 2016 election. If these voters are not bound to vote along with the electoral college decision, they're theoretically also not bound to vote along with the determination of the compact, which creates even
more uncertainty. Additionally, I guarantee you if the compact needs to be used during this election, it
will be taken to the supreme court.
TL;DR: We use the census to divide representative seats, and we use representative seats for electoral college votes, and the electoral college might be subverted because of a new interstate compact. All of this is happening in the 2020 election cycle. It's a fucking mess.