Other forms: battlegrounds
A battleground is a piece of land on which a war or battle is fought. You can visit many of the battlegrounds of the US Civil War.
The literal meaning of battleground is just what it sounds like: the ground on which a battle has been waged. You can also use the word for the site of a figurative battle, like an election or a vote on a controversial issue. "Battleground states" are those in which the vote between two parties could swing either way, since neither holds a firm majority.