A surprise party is a party that is not made known beforehand to the person in whose honor it is being held.
Birthday surprise parties are the most common kind of surprise party. At most such parties, the guests will arrive an hour or so before the honored person arrives. Often, a friend in on the surprise will lead the honored person to the location of the party without letting on anything.
The guests might even conceal themselves from view, and when the honored person enters the room, they leap from hiding and all shout, "Surprise!" For some surprise birthday parties, it is considered to be a good tactic to shock the honored person. Streamers, silly string, and balloons may be used for this purpose. Evidence of a party, such as decorations and balloons, are not made visible from the exterior of the home, so that the honored person will suspect nothing.
Early discussions of the concept include a section of Rambles in America, past and present, published in 1890, and an account of a "impromptu soiree" in 1850, described later in the text as a surprise party. The term previous had military attack meaning