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  "body": "\n## Summary\n\nAn algebraic stack is a generalization of an algebraic space in which points may have automorphism groups.\nFormally it is a stack in groupoids over the category of schemes that admits a smooth surjection from a scheme.\nAlgebraic stacks are the natural home of moduli problems, such as the moduli of curves, where the objects classified have nontrivial symmetries.\n\n## Explanations\n\n### L1 human\n\nA moduli space should have one point for each object of a given kind, for example each curve of genus $g$.\nWhen objects have symmetries, no ordinary space can do this job well: families get glued in ways that lose information.\nA stack keeps track of the symmetries by remembering, for each point, a group of automorphisms.\nThe simplest example is the classifying stack $BG$ of a finite group $G$: it has one point, with automorphism group $G$.\n",
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