What Is Meant by the Term "Battleground State

What is meant by the term "battleground state"?

A) The state cannot be considered safely Democrat or Republican so either party has a chance of winning that state in the presidential election.
B) Party politics are so strong in the state that nearly all efforts to move forward are met with huge battles.
C) The majority of the voters in the state are ideologically moderate.
D) A state that splits its distribution of votes in the electoral college.
E) Election results in such states are normally decided within the courts weeks after the election.