The phrase "extrasolar planets" refers to planets that exist outside of our own solar system. They are planets that orbit around stars other than our Sun. Full definition
The HDST could finally answer the question of whether humans are alone in the Universe, by directly probing the atmospheres of dozens of extrasolar planets for signs of life. (scientificamerican.com)
«Now that we have some hold on what the original moons of Neptune were like, that can give us some clue as to what we should expect for extrasolar planets of that type,» says Matija Cuk at the SETI Institute. (newscientist.com)
His research focuses on extrasolar planet searches and characterization. (project-eden.space)