An inflection was a change in pitch in an individual's voice. It was a common characteristic of languages. One common misconception was that all Rateg spoke with the same particular inflection. (TNG: "Unification I")
Inflections could often give clues as to a person's origins. In 2153, Hoshi Sato surmised that MACO soldier N. Kemper came from Duluth, saying there was plenty of the city's influence evident in his inflections. (ENT: "The Xindi")
Inflections could also indicate emotion. In 2153, after Trip Tucker cited T'Pol's voice tensing up as an indicator of her supposed jealousy about him and Corporal Amanda Cole, she responded by saying, "I didn't know you were an expert in vocal inflections". (ENT: "Harbinger")
In 2366, Kivas Fajo marveled over Data's voice simulation, including the inflections. (TNG: "The Most Toys")
Hidden meanings could be transmitted by inflections. In 2370, Deanna Troi analyzed a transmission from William T. Riker, including inflections, but found nothing. (TNG: "Gambit, Part II")
Some inflections were unique to individuals. In 2373, Kathryn Janeway used Captains Amasov and Picard's inflections while reading passages from their logs about the Borg. Chakotay mentioned this to her after she finished, surprising Janeway, who wasn't aware she was doing so. (VOY: "Scorpion")