spec·trum (spĕkˈtrəm)

1. The distribution of a characteristic of a physical system or phenomenon, especially the distribution of energy emitted by a radiant source arranged in order of wavelengths.
2. The color image presented when white light is resolved into its constituent colors: red, orange, yellow, green, blue, indigo, violet.
3. The plot of intensity as opposed to wavelength of light emitted or absorbed by a substance, usually characteristic of the substance and used in qualitative and quantitative analysis.
4. The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses.
5. The group of pathogenic organisms against which an antibiotic or other antibacterial agent is effective.