The term Spectral Band can be used in a general way to indicate a contiguous set (interval) of spectral Wavelengths.
It also has a more specific meaning: such an interval of wavelengths that are affected by a molecule, often a large, complex molecule, that produces many Spectral Lines, often forming a closely-packed pattern, even to the point of overlapping. If they overlap or if the Spectroscope's Resolution is low, it is seen as a range of Absorption (Absorption Band) or Emission (Emission Band).
Polycyclic Aromatic Hydrocarbons produce these, e.g., PAH Emissions. Water Lines are another example.