Any piece of the landmass that is surrounded by water bodies, is called an island or isle. Therefore, an island is smaller than a continent and surrounded entirely by water. Although most islands are formed naturally, others are artificial islands, constructed by people. Islands occur in rivers and lakes, although the largest islands are found in oceans or seas. These islands vary in sizes, shapes, flora, fauna, climate, and geography.
Figuring out the exact number of islands on Earth can be a difficult process, because not all islands have been discovered. Quite a few islands around the world are very large, and many of them are countries. Although continental landmasses are surrounded entirely by water, they are not islands because of their massive sizes. The man-made Suez and Panama canals are disregarded, as they were not natural waters that separate the continents.
Here are the top 20 largest islands in the world.
| Rank | Island | Size |
| 1. | Greenland | 2,130,800 km2 (822,700 sq mi) |
| 2. | New Guinea | 785,753 km2 (303,381 sq mi) |
| 3. | Borneo | 748,168 km2 (288,869 sq mi) |
| 4. | Madagascar | 587,041 km2 (226,658 sq mi) |
| 5. | Baffin Island | 507,451 km2 (195,928 sq mi) |
| 6. | Sumatra | 443,065 km2 (171,068 sq mi) |
| 7. | Honshū | 225,800 km2 (87,200 sq mi) |
| 8. | Victoria Island | 217,291 km2 (83,897 sq mi) |
| 9. | Great Britain | 209,331 km2 (80,823 sq mi) |
| 10. | Ellesmere Island | 196,236 km2 (75,767 sq mi) |
| 11. | Sulawesi | 180,681 km2 (69,761 sq mi) |
| 12. | South Island | 145,836 km2 (56,308 sq mi) |
| 13. | Java | 138,794 km2 (53,589 sq mi) |
| 14. | North Island | 111,583 km2 (43,082 sq mi) |
| 15. | Luzon | 109,965 km2 (42,458 sq mi) |
| 16. | Newfoundland | 108,860 km2 (42,030 sq mi) |
| 17. | Cuba | 105,806 km2 (40,852 sq mi) |
| 18. | Iceland | 101,826 km2 (39,315 sq mi) |
| 19. | Mindanao | 97,530 km2 (37,660 sq mi) |
| 20. | Ireland | 84,421 km2 (32,595 sq mi) |
Have been searching this for long thanks @victor mochere