bay 指海岸线上一大块凹入的地方，是港口的所在地。
gulf 一般比bay大，但比sea小。指大片深入到陆地中，由海岸围绕成半圆形的海水区域。
参考例句
1. The gulf extends northward. 海湾向北方延伸。
2. Are children our feeble bridge over the gulf of death? 在死的海湾上方孩子是我们的虚弱的桥吗？
3. Thomas Hudson looked out at the flatness of the blue sea and the darker blue of the Gulf. 托马斯·赫德森呆望着湛蓝的海面，海面水平如镜。在海湾那儿，都是深蓝一片了。
英英解释
n.
1. an arm of a sea or ocean partly enclosed by land; larger than a bay
2. an unbridgeable disparity (as from a failure of understanding)
3. a deep wide chasm
