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what does the term nap mean in horse racing
A tip that is considered as a racing certainty, almost completely certain to be true, is also called a nap and tipsters in newspapers will tend to indicate the nap.
is the term Nap used only in one sport
In the past tipping was mostly associated with horse racing but can apply to any sport that has odds offered on it.

Question: What is the origin of the term
Self-contained rewrite: What is the origin of the term Nap