Final answer:
Cold clouds of gas and dust between stars are called molecular clouds, which play a key role in star formation.
Step-by-step explanation:
Cold clouds of gas and dust between stars are called molecular clouds. These clouds are significant because they have cold interiors with temperatures only around 10-20 K. Most of their gas atoms are bound into molecules, making them dense regions in interstellar space, comprising roughly 30% of the total mass of gas between the stars. In these cold clouds, the majority of the gas is in the form of atomic hydrogen. Molecular clouds are the birthplaces of most stars in our Galaxy, making them incredibly important in the study of star formation and the structure of galaxies.