They loom large in any coverage of the United States presidential election: the coveted “swing states”.

Upon the rocky shoals of a small number of fiercely contested states, the dreams of many aspiring national figures have been dashed and splintered.

As their name implies, swing states — also known as battleground states — have the potential to sway the outcome of a national election.

This year looks no different, with Vice President Kamala Harris and former President Donald Trump locked in a tight battle in a number of must-win states.

But what is a swing state? And why do they play such an outsized role in presidential races? We answer these questions and more in a brief explainer.

What does the term ‘swing state’ mean?

A swing state refers to a small group of states that are narrowly contested in presidential races.

In US politics, presidential elections are decided by a weighted voting system known as the Electoral College, not by the popular vote. Because of that, swing states can play an outsized role in deciding the outcome.

Each of the 50 states are apportioned a certain number of Electoral College votes, in proportion to their population size. A presidential candidate must secure 270 electors to win.

Since most states vote consistently with one party or another, a small number of swing states can determine victory or defeat. Candidates therefore tend to invest a great deal of resources in courting voters in those states, as opposed to party strongholds.

Which states are considered swing states?

One of the defining characteristics of a swing state is its ambiguous political leanings. But states that were once contested can start to tilt towards one party or another.

For this reason, swing states can change. Florida, for example, was considered a swing state from the 1990s through 2020, but it is now seen as reliably red, as Republican voter registration grows.

This year, the states being closely watched are Arizona, Georgia, Michigan, Pennsylvania, Wisconsin, Nevada and Minnesota. New to this clutch of swing states is North Carolina.

What can polling tell us about swing states?

True to form, the swing states in this election cycle show Trump and Harris in a narrow race.

In Arizona, for instance, polling averages found the two candidates virtually tied, or Trump edging out a thin advantage of one point or less.

Meanwhile, in Pennsylvania, the race is also in dead heat, with polling averages showing a tie or Harris ahead by less than 1 percent.

Minnesota is the only one of the potential swing states where Harris maintains a healthy lead, ahead of Trump by an average of between five and eight points.

While voter sentiment could still change in the weeks ahead, these averages point to a race with a close finish when voters go to the polls in November. Meanwhile, both Harris and Trump have been campaigning heavily in states like Pennsylvania, Michigan and Georgia, hoping to tilt the states to their side.