A zip bomb is a tiny zip file that will become much larger when extracted. You can dowload them here!
You should probably not extract them, though. They are more than 300 gigabytes when extracted.
I have two for dowload. One of them was zipped, and one of them was tarred, gzipped, then xzed. The latter is MUCH smaller than the regular zip bomb, but less people will be able to extract it.
Smaller/bigger does NOT refer to the size when extracted. It refers to the size when compressed.