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A range; a continuous, infinite, one-dimensional set, possibly bounded by extremes.
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Specifically, a range of colours representing light (electromagnetic radiation) of contiguous frequencies; hence electromagnetic spectrum, visible spectrum, ultraviolet spectrum, etc.
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The autism spectrum.
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The pattern of absorption or emission of radiation produced by a substance when subjected to energy (radiation, heat, electricity, etc.).
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The set of eigenvalues of a matrix.
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Of a bounded linear operator A, the set of scalar values λ such that the operator A—λI, where I denotes the identity operator, does not have a bounded inverse; intended as a generalisation of the linear algebra sense.
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(abstract algebra) The set, denoted Spec(R), of all prime ideals of a given ring R, commonly augmented with a Zariski topology and considered as a topological space.
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Specter, apparition.
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The image of something seen that persists after the eyes are closed.