They say cocktail hour starts at 4. A cocktail party organised for purposes of social or business networking is called a mixer.
The look it is neither formal nor casual and it is a look that many men have adopted to cover the advent of both business or play breaking out. The Blazer, a pair of Flannels (or chinos) and either a shirt and tie or a polo.
Although it has been said that the inventor of the cocktail party was Alex Waugh of London an article in the St Paul Pioneer Press in May 1917 credited its invention to a certain Mrs. Julius S. Walsh Jr. of St. Louis Missouri. Mrs. Walsh invited 50 guests to her house on a Sunday at high noon for a one-hour affair. "The party scored an instant hit," the newspaper declared, and stated that within weeks cocktail parties had become "a St. Louis institution".