"hydrothermal" refers to something related to both water and heat. It specifically describes processes or environments that involve hot water and its interactions with rocks and minerals. Full definition
In spring 2015, MBARI researchers discovered a large, previously unknown field of hydrothermal vents in the Gulf of California, about 150 kilometers (100 miles) east of La Paz, Mexico. (sciencedaily.com)
«New kind of hydrothermal vent system found in Caribbean.» (sciencedaily.com)
The paper from researchers with the Cassini mission, published in the journal Science, indicates hydrogen gas, which could potentially provide a chemical energy source for life, is pouring into the subsurface ocean of Enceladus from hydrothermal activity on the seafloor. (sciencedaily.com)