What does Judges 9:47 mean?

In bloody revenge, Abimelech is destroying the city and people of Shechem. The city leaders had turned against him and plotted to overthrow him (Judges 9:22–25). Abimelech defeated those leaders in battle (Judges 9:38–41). Not content to leave it at that, Abimelech has declared total war. In English, his tactics are sometimes called "scorched-earth," meaning the goal is to obliterate people, buildings, and agriculture alike. Abimelech and his men destroyed everything and everyone except for the defensive tower and the temple to El-berith (Judges 9:42–46). The leaders of the tower have locked themselves into the temple, a structure that had stood for hundreds of years.

These last leaders of Shechem have taken refuge in the "stronghold" of the temple, along with the rest of the survivors. This likely means some kind of underground cave or room that could be secured against an attacker. About a thousand people, are in this stronghold, but Abimelech has a plan to finish them all (Judges 9:48–49).