They differ in their wavelength. A Black body is defined to be a perfect absorber and emitter of radiation. A Black body curve looks like Fig. 2.9 on page 52 of Chaisson and McMillan. The intensity of radiation decreases towards both lower and higher ends of the frequency. The intensity peaks at a certain frequency, characterized by the Black body's temperature, irrespective of it's shape, size and material.
Black body curves at various temperatures never intersect each other.
When a beam of light passes through a relatively cooler gas, certain frequencies characteristic of the gas atoms or molecules are absorbed. The resultant spectrum then demonstrates dark lines or bands on a continuous background. It is known as an absorption spectrum. When an electron absorbs energy, it goes into an excited state. The atom with an electron in the excited state is called an excited atom.