Oganesson (Og) is a chemical element with atomic number 118. It is the heaviest known element, and it's the last element in the periodic table.
Oganesson is named after the Russian nuclear physicist Yuri Oganessian, who was leading the experiment where the element was first produced. Like the other superheavy elements, oganesson is a synthetic element which does not occur naturally on Earth but must be produced through human manipulation of the atomic nucleus, such as via particle accelerators. Oganesson has a half-life of less than one millisecond, only a few atoms of it have ever been created, which means it's very hard to know its chemical properties. Technically oganesson belongs to the group called noble gases, but it may not even be a gas.