Think back to a fond time and place in your childhood — perhaps a stroll with a parent along a waved-washed beach. The memory is a happy (and likely idealized) one, but still tinged with the bittersweet knowledge that you can never go back.

It's a complex emotion we know as nostalgia.

People experience it for their lost youth, first love and some even pine for a time they never experienced. That feeling is especially potent this time of year, as the holidays creep in.

As part of NPR's Word of the Week series, we take a look at nostalgia, its origin and how it was transformed from a 17th century malady to a 21st century marketing strategy.

It started with homesick soldiers

During the 1600s, Europe was gripped by a series of major conflicts — the Thirty Years' War, the Franco-Du

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