In Genesis, Noah received an olive leaf from the dove as evidence that the floodwaters were receding.
After Noah first sent out a raven, he sent a dove to test whether the waters had diminished. The dove returned because it found nowhere to land. Seven days later, Noah sent it out again, and the bird came back in the evening carrying a freshly plucked olive leaf.
That small leaf showed Noah that vegetation was visible above the water and that the flood was no longer covering the land in the same way. Noah waited another seven days before sending the dove out once more; this time it did not return.
The olive leaf later became a widely recognized symbol of peace and hope. The biblical passage, however, presents it first as practical evidence about the landscape after the flood. It is specifically an olive leaf, not a generic green branch or a leaf from another tree.