What is it called when a district has no sitting legislator running for reelection?

Question

Quizplus · Accepted Answer

An open seat refers to a district where there is no sitting legislator running for reelection, leaving the seat "open" for candidates to compete for. Option B, a closed seat, is not a common political term. Option C, a safe seat, refers to a district where the incumbent is likely to win reelection due to a history of strong support from the district's voters. Option D, a contested seat, refers to a district where the election is expected to be competitive, regardless of whether there is a sitting legislator running for reelection or not.

What Is It Called When a District Has No Sitting