This system was established in a year 2000. This system is some sort of a map that tells us how much are American states liberal or conservative.

Patterns within states reveal that the reversal of the two parties geographic bases has happened at the state level, but it is more complicated depending on urban/rural divides associated with many of the largest changes.

We also cannot forget that if the state colour is darker, the more is the state being liberal (democrats) or conservative (republicans). This graph or map shows states preference of being one of those two parties:

For becoming a president, you need 270 electoral votes to win. Biden won with 279 electoral votes. It looks like the map is mostly red, but we cannot forget that if the colour is paler it is not a safe for that party. It just leans towards that party.

Finally, we can see that some states have a brownish colour. The states which have that colour are called toss-ups. Toss-up means that the state is not sure who to vote so their vote are not helpful for any of the parties.