giant molecular cloud; GMC
Technical term in astronomy for a large, dense cloud of molecular gas, often a site of star formation.
A giant molecular cloud extends across the constellation Orion.
Giant molecular clouds are known as sites of star formation.
分子雲 is a broader term for any molecular cloud, while 巨大分子雲 specifically refers to the largest examples, often called GMCs.
Compound of 巨大 (きょだい, 'giant') + 分子 (ぶんし, 'molecule') + 雲 (うん, 'cloud'). A direct translation of the English astronomical term 'giant molecular cloud'.