Pseudoword

A pseudoword or non-word is a unit of speech or text that appears to be an actual word in a certain language, while in fact it has no meaning in the lexicon. It is a kind of non-lexical vocable.

Such words without a meaning in a certain language or no occurrence in any text corpus or dictionary can be the result of (the interpretation of) a truly random signal, there will usually be an underlying deterministic source as is the case for:

When nonsensical words are stringed together, gibberish may arise. Word salad in contrast may contain legible and intelligible words but without semantic or syntactic correlation or coherence.

Within linguistics, a pseudoword is defined specifically as respecting the phonotactic restrictions of a language. That is, it does not include sounds or series of sounds that do not exist in that language: it is easily pronounceable for speakers of the language. Also, when written down, a pseudoword does not include strings of characters that are not permissible in the spelling of the target language. "Vonk" is a pseudoword in English, while "dfhnxd" is not. The latter is an example of a nonword. Nonwords are contrasted with pseudowords in that they are not pronounceable and by that their spelling could not be the spelling of a real word.

Pseudowords are also sometimes called wug words in the context of linguistic experiments. This is because wug [wʌg] was one such pseudoword used by Jean Berko Gleason in her wug test 1958 experiments. Words like wug, which could have been a perfectly acceptable word in English but isn't due to an accidental gap, were presented to children. The experimenter would then prompt the children to create a plural for wug, which was almost invariably wugs [wʌgz]. The experiments were designed to see if English morphophonemics would be applied by children to novel words. They revealed that even at a very young age, children have already internalized many of the complex features of their language.

...
Wikipedia