Seven states are expected to play a key role in electing the next president of the United States: Arizona, Wisconsin, North Carolina, Georgia, Michigan, Nevada and Pennsylvania.

So what is a battleground state, and why is their voice so important?

There are 538 Electoral College votes distributed among the 50 states and the District of Columbia. Each state gets at least three votes, depending on the size of its congressional delegation.

Congressional seats are allocated to each state based on their population. So the smallest states get three votes in the electoral college (they have two senators and one member of Congress). Washington, DC, also gets three. The most populous states get much more: California gets 54 electoral votes (it has two senators and 52 congressional districts), Texas has 40, Florida has 30, New York has 28 and so on.

In almost all states, the winning candidate receives all the electoral votes. Whichever candidate receives 270 or more electoral votes becomes president.

Some states are historically blue (where Democrats dominate) or red (where Republicans dominate). Battleground states are states where voters do not consistently vote for the same party, but battleground states can change from election to election.

The larger battleground states, like Pennsylvania, have more congressional seats and are therefore especially important in a candidate’s journey to 270. And if a candidate wins three or more battleground states, they are more likely to win the election.

Therefore, the seven battlegrounds could determine who becomes president.

Read more about how US elections work.