A hovercar was a car that utilized some form of gravity manipulating technology to "hover" over the ground, and drive through streets similar to Earth automobiles. Tom Paris explained to Harry Kim that hovercars first came into general use on Earth circa 2030s. (VOY: "The 37's")
As Kim thought the 1936 Ford truck was an early hovercar, Paris stated that he was about a century too early for that.
When Captain Archer was brought back ten months to his apartment by Daniels, he looked out his window into the city and saw hovercars flying by. (ENT: "Shockwave")
In 2259 of the alternate reality, Thomas Harewood owned a hovercar, and he drove himself and his wife to the Royal Children's Hospital to see his terminally ill daughter. (Star Trek Into Darkness)
When Benjamin Sisko was about four years old, his biological mother, Sarah Sisko, who had left him and his family, died in a hovercraft accident in Australia. Joseph Sisko never told his son this until 2375. (DS9: "Image in the Sand")
In 2371, when the USS Voyager brought aboard an old automobile, Harry Kim mistook it for an early hovercar. (VOY: "The 37's")