Why Don't Hotels Have A 13th Floor?

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Why Don't Hotels Have A 13th Floor?
There's a word for why that is: triskaidekaphobia.

Hotels in cities big and small have seemingly picked up on a longtime superstition. 

They'll skip over the not-so-lucky number 13 and go straight from 12 to floor 14. 

There's a word for why that is: Triskaidekaphobia.

But what does that mean?