Invented words that still sound English, built from onset, vowel and coda patterns instead of letters thrown together at random.
Random letters do not produce words. They produce strings like ktzqr that no English speaker can pronounce. What makes an invented word feel real is following the rules for how sounds combine, which linguists call phonotactics. Every syllable here is built as an onset, a vowel nucleus and an optional coda, drawn from clusters that actually occur in English: br and str are valid onsets, tk is not; nd and sk are valid codas, qv is not. Assembling syllables from those pieces means every result is pronounceable on sight, which is the entire difference between a usable invented word and noise.
Syllable count controls the register of the result more than anything else. Two syllables gives you the short, punchy shape most modern product names use and the form most likely to be available as a domain. Three is the sweet spot for names that need to feel substantial without being a mouthful. Four and above starts to sound like a pharmaceutical or a fictional place name, which is sometimes exactly what you want, invented languages and fantasy settings need longer forms to feel like a real vocabulary rather than a list of brands.
Because each syllable is assembled from consonant clusters and vowels that actually occur in English, rather than from letters picked at random.
Occasionally, especially at one or two syllables. Always search before committing an invented name to anything permanent.
Two or three. Two is punchy and more likely to be available; three feels more substantial. Four and above reads as pharmaceutical or fantasy.