A pseudoword 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. It is a specific type of nonce word, or even more narrowly a nonsense word, composed of a combination of phonemes which nevertheless conform to the language's phonotactic rules. It is thus a kind of vocable: utterable but meaningless.
Such words lacking a meaning in a certain language or absent in any text corpus or dictionary can be the result of (the interpretation of) a truly random signal, but there will often be an underlying deterministic source, as is the case for examples like jabberwocky and galumph (both coined in a nonsense poem by Lewis Carroll), dord (a ghost word published due to a mistake), ciphers, and typos.