What is negative alpha?

Excuse me, but could you please clarify what is meant by the term "negative alpha" in the world of finance and investments? I'm particularly interested in understanding how it relates to the performance of a portfolio or investment fund, and what it indicates about the manager's ability to outperform a benchmark or index. Is it a sign of underperformance, or does it have other implications that I should be aware of? I'm looking for a concise explanation that helps me grasp the concept quickly. Thank you.