States that usually lean towards a single party are called safe states, as it is generally assumed that a candidate has enough support to draw up a sufficient share of voters in the election.
The main swing states right now are Arizona, Colorado, Florida, Georgia, Iowa, Maine, Michigan, North Carolina, Ohio, Pennsylvania, Texas and Wisconsin.
Mr Biden is currently leading in all swing states except Ohio and Iowa, where Mr Trump has a 0.5 and two percent lead, respectively.
The state of Florida has proved a reliable indicator in recent elections.
The southern state has a diverse population, but is generally conservative-leaning and has a high population of older voters.