Where the words come from
Recession, depression, peak and trough defined, the business cycle as movement from peak to trough and trough to peak, and unemployment as a lagging indicator of business activity — Principles of Economics 2e, OpenStax, licensed CC BY 4.0. https://openstax.org/books/principles-economics-2e/pages/19-3-tracking-real-gdp-over-time and https://openstax.org/books/principles-economics-2e/pages/21-introduction-to-unemployment. Changes: "We call the highest point of the economy, before the recession begins, the peak" and "the lowest point of a recession, before a recovery begins, is the trough" recast as card definitions; the US NBER record and Table 19.7 dropped; 2008 recession timing kept from the Chapter 21 introduction; the boom card, the UK two-quarter convention, the chart and the labels Y1 to Y3 and t1 to t3 are ours; British spelling.
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