seriously this command WILL CRASH servers if you run it. if you run this on singleplayer it will crash upon exiting the world.
for the love of god don't run this on any world that you want to keep unless you seriously know what you are doing
what this command does is:
makes all entities set every entity on fire for 50000 seconds, and makes all those entities run the command, and makes those entities run the command and does this repeating 5 times