What is the difference between an island and a peninsula?

The main difference is that the islands are completely isolated from the continents. That is, they did not have a land border with larger land formations, but were surrounded by water on all sides. If they are located close to land, then the section of the sea between the island and the mainland is called a strait. The largest island is Greenland.
The peninsula must have a connection with the land. Thin natural bridges that connect the peninsula to the land are called isthmuses. The largest is the Arabian Peninsula.