There is only one file type that uses the .MCWORLD extension:
Minecraft World Backup File
A MCWORLD file contains behavior and resource files that make up a world in Minecraft (Bedrock Edition), a popular block-building game. It stores multiple files, such as .DAT and .TXT files compressed with ZIP compression. MCWORLD files are typically used to backup a world or transfer a world to another Minecraft user.
MCWORLD files may be created by a program such as Minecraft Launcher, (MinecraftSP.exe) a custom application launcher for Minecraft. They may also be created by a user when he zips the world files into one .ZIP file then renames the extension from ".zip" to ".mcworld".
Since MCWORLD files are saved in a ZIP format, they can be expanded using a Zip decompression utility. The MCWORLD file can also be opened in Infdev, which is the third phase in Minecraft's development cycle and is only playable in single player Survival mode. You can access it by selecting "New Profile" and "Allow infdev" in Minecraft.
Updated: March 10, 2019