The term "Novan" was used to describe a group of Human colonists who settled the planet Terra Nova and their descendants. The term was applied to these colonists in much the same way the term Martian was applied to those living on Mars.
The Terra Nova colony was the first Human colony outside the Sol system, founded in 2078 by the SS Conestoga after a nine-year flight from Earth. The Novans were successful in establishing a fully-functioning community on a world in deep space so a second ship of colonists heading to Terra Nova was planned.
The Novans were not interested in sharing their home they had struggled to build. Led by a man named Mark Logan, the situation with Earth became severely strained, with Logan transmitting threats of violence upon any starships that would arrive in orbit of his planet. This was the last message received from Novans. Earth lost contact with them, and never launched a ship to investigate because of limited resources. The fate of the Novans remained a mystery.
In 2151, the Earth starship Enterprise NX-01 visited Terra Nova to discover the whereabouts of the apparently missing colony. They discovered the irradiated remains of the colony, and it was determined that the colony had been destroyed by an asteroid impact, which had scattered radioactive debris over the northern hemisphere. The Novans that survived the asteroid impact took refuge in underground caverns in order to avoid the radiation on the surface. Because their earliest memories involved Mark Logan's threats, they established the belief that they were not Human, and Humans attacked them with the "poison rain" because they didn't want to share their home. This belief was passed on to the next generations. When a landing party descended on the planet, Novans attacked the "Human" intruders.
Eventually, the Enterprise crew was able to gain the trust of the Novans, convincing them that Earth was not responsible for destroying the original colony. As the underground water supply the Novans used to survive had slowly become contaminated by the surface radiation, the Novan population was eventually relocated to a continent on the southern hemisphere that was unaffected by the fallout from the asteroid impact. (ENT: "Terra Nova")
The Novans had developed some special slang or expressions. Overside was the name of the planet's surface; while Underside were the underground caverns, their contemporary dwelling; they referred to Enterprise as a Sky Ship. To refer to hunger they used the expression hollow stomach; the ancestors were referred as before-family; the radioactive devastation caused by the asteroid was remembered as poison rain.
Illustrator John Eaves, who designed the Conestoga, reckoned that the Humans who went on to become Novans were asleep while aboard the Conestoga during its nine-year journey from Earth to Terra Nova. 
Hair Designer Michael Moore used colored hair conditioner to simulate mud that supposedly packed the Novans' hair. Their hairstyles turned out be one of Moore's favorites from the first three seasons of Star Trek: Enterprise. (Star Trek: Communicator issue 152, p. 31)