A massive solid planet is a planet which is a planet that has similar mass to a Gas giant, however it maintains a terrestrial and or solid surface instead of a liquid surface.
In 2014, new measurements of Kepler-10c found that it was a Neptune-mass planet (17 Earth masses) with a density higher than the Earth's, indicating that Kepler-10c is made mostly of rock with possibly up to 20% high-pressure water-ice but without a hydrogen-dominated envelope. As it is well above the 10 Earth mass upper limit that is commonly used for the term "super-Earth" the term mega-Earth has been proposed. A similarly massive and dense planet could be Kepler-131b, although its density is not as well measured as that of Kepler-10c. The next most massive known solid planets are half this mass: 55 Cancri e and Kepler-20b.
Gas giants can also have large solid cores: the Saturn-mass planet HD 149026 b has only two-thirds of Saturn's radius so it may have a rock-ice core of 60 Earth masses or more.