It's when posters became nostalgic and wax romantically about the "classy" movie stars of Hollywood's Golden Age, compared to the "trashy" stars of today.
There was just as much adultery, alcoholism, drug use, wild partying, out of wedlock children, petty crime, drunk driving, and miscellaneous bad behaviors then.
But the studios had departments and staff to keep much of it out of general public view.
They were not always successful, with stories ending up in tabloids (Confidential was great on disclosing many back street shenanigans) and rumors eventually reached the average moviegoers.