A spectrum (plural spectra or spectrums ) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by analogy to many fields other than optics. Thus, one might talk about the spectrum of political opinion, or the spectrum of activity of a drug, or the autism spectrum.

Tarang..

A. The distribution of energy emitted by a radiant source, as by an incandescent body, arranged in order of wavelengths.
b. The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses

A range of values of a quantity or set of related quantities.
b. A broad sequence or range of related qualities, ideas, or activities:

in telecom

The word spectrum refers to a collection of various types of electromagnetic radiations of different wavelengths