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  "body": "\n## Summary\n\nA spectrum, in algebraic topology, is a sequence of pointed spaces $E_n$ with maps from the suspension of each space to the next one.\nSpectra are the objects of stable homotopy theory, much as spaces are the objects of unstable homotopy theory.\nEvery [[generalized cohomology theory|H28PSZR7XG]] is represented by a spectrum, and spectra have homotopy groups in all integer degrees, including negative ones.\n\n## Explanations\n\n### L1 human\n\nA space can be suspended again and again, and a spectrum is what one gets by allowing the process to run in both directions.\nIt is a list of spaces $E_0, E_1, E_2, \\ldots$ in which each space is glued to the next by a map from its suspension.\nThe simplest example takes $E_n = S^n$, the $n$-sphere, with the identity maps $\\Sigma S^n = S^{n+1}$; this is the sphere spectrum.\nAnother example uses Eilenberg–MacLane spaces $K(G, n)$, and it gives ordinary cohomology with coefficients in $G$.\n",
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