居中 is a formal verb phrase with two core uses: (1) spatially or positionally 'to be in the middle', often in contexts like alignment or arrangement; (2) figuratively 'to act as an intermediary' in disputes or negotiations. In the first sense you'll see it in 居中排列 (center-align) or 居中位置 (central position). In the second sense it typically pairs with verbs like 调解 (mediate) or 斡旋 (broker), forming 居中调解 (mediate between parties). It is not used in casual conversation — it's a written or formal register word.