There are many definitions of an Earth-like exoplanet. Some say it’s a planet that orbits a star at just the right distance for liquid water to exist on its surface. Some say it’s a rocky planet, like ours. But determining if an exoplanet is truly habitable requires actually figuring out what’s on the planet.
Source: Gizmodo – When Will We Finally Find a Truly Earth-Like Exoplanet?