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  "body": "\n## Summary\n\nA measure on a measurable space is a function that gives each measurable set a size in $[0, \\infty]$.\nIt gives the empty set size $0$ and is countably additive: the size of a countable disjoint union is the sum of the sizes.\nMeasures generalize length, area, volume, counting and probability, and they are the basis of the Lebesgue integral.\n\n## Explanations\n\n### L1 human\n\nA measure is a consistent way to give sizes to sets.\nIf a set is cut into countably many separate pieces, its size is the sum of the sizes of the pieces.\nLength on the real line is a measure: the interval $[0, 2]$ has size $2$, the union of $[0, 1)$ and $[1, 2]$.\nCounting the elements of a set is also a measure, and so is probability.\nSizes may be infinite, as for the length of the whole line.\n",
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