In the Noah's Ark story, the dove returned with an olive leaf to show that the floodwaters were receding.
Genesis 8 says Noah first sent out a raven and then sent a dove. On its second release, the dove came back in the evening carrying a freshly plucked olive leaf. Noah understood this as evidence that the waters had gone down from the earth's surface.
The dove's return is not the final moment of the flood narrative. Noah sent the dove out again later, and it did not return, indicating that the land had become more suitable for departure. Only afterward did Noah remove the covering of the ark and eventually leave it.
The olive branch or olive leaf later became a widely recognized symbol of peace. In the Genesis passage, however, its immediate role is practical: it provides Noah with information about the changing landscape after the flood.