Pronunciation was the way a word or name was to be vocalized. A document which showed how to pronounce words was called a pronunciation guide. (ENT: "A Night in Sickbay")

In 2267, after Leila Kalomi remarked that Spock had never told her his other name, Spock assured her that she couldn't pronounce it. (TOS: "This Side of Paradise")

According to Sybok, the Andorian name for Sha Ka Ree was unpronounceable. (Star Trek V: The Final Frontier)

In 2364,The Traveler explained that he was listed only as Mister Kosinski's assistant because his name was unpronounceable to most Humans. (TNG: "Where No One Has Gone Before")

One common pronunciation error was metathesis. (TNG: "Hollow Pursuits")