It's annoying that the media keep referring to the extramarital activities of people like Tiger Woods as "affairs". An example might be an actress who had "affairs" with 3 of her last 4 leading men. Or a husband who picked up a woman on a business trip.
In my view, an affair is " a romantic or passionate attachment" of some duration. Not a just a f___, or "quickie". Here's a recent example:
"Nikki Haley Denies Second Rumored Affair" responding to -
"South Carolina lobbyist Larry Marchant said Wednesday that he had a one-night stand with Haley during a 2008 trip to Salt Lake City for a conference on school choice."
Media: Even though a bit tricky, call it what it is!
Related is misuse of the word "mistress" A common definition is :"a woman other than his wife with whom a married man has a continuing sexual relationship, often with continuing financial support" A night with a cocktail waitress does not make her a mistress.