nonce word
Hapax legomenon
Literary nonsense
Metasyntactic variable
Placeholder name
Pseudoword
sniglet
Examples of nonce-word articles
Foobar
Glokaya kuzdra
Gostak
Jabberwocky
Pompatus
Protologism
Runcible
Supercalifragilisticexpialidocious
https://en.wikipedia.org/wiki/Nonce_word