桥头堡

qiáo tóu bǎoqiaotoubao

1. bridgehead (military)
2. stronghold serving as a base for advancing further into enemy territory
3. bridge tower (ornamental structure at either end of a bridge)
4. (fig.) gateway (place that provides access to other places beyond it)
5. bridgehead (key location serving as a base for further expansion)

Study it in Yanamino