An olive wreath is a kind of circle made out of olives. It's like making a necklace out of fruits that are called olives, which are kind of like small round grapes that are green or black.
The wreath is made by taking a bunch of olives and wrapping them around a wire or a flexible stick. You keep adding more and more olives and twisting them together until you have a big circle of olives all around.
In ancient Greece, people used to make these olive wreaths and give them to people who did really well in competitions or battles. It was like a prize or a special gift to say congratulations!
Even today, olive wreaths are still used in some places, especially during events like the Olympics, to honor people who have done something great.