“岛屿”是被海水或湖水围着的一块块陆地，可以很大，也可以很小。

"岛屿" are pieces of land surrounded by sea or lake water, which can be large or small.

这个词比“岛”更书面一些，常用来说很多岛。

This word is more formal than "岛" and is often used to refer to many islands.