Soubresaut in modern French can mean a sudden start, a spike, a jolt, or a blip in data.  When you think of soubresaut as a line of data on a graph, imagine that the data continues in a steady line and then suddenly spikes higher only to fall back to its initial flat line.  Now, picture the dancer springing into the air and landing back in their plié.  The similarity of movement is clear: a forceful spring followed by a descent.

You could also imagine the "sudden start" as the everyday version of the ballet action.  Someone comes up behind you unexpectedly causing you to jump in surprise before realizing that it is an old friend.  The sudden jump is comparable to the springing ballet action.

The origin of soubresaut also helps to describe the movement.  Soubre is the Old French version of sur meaning "on top of."  Saut means to jump.  A soubresaut means a jump on top of itself, which again supports the image of the startle reaction.

Soubresaut pronounced [subʀəso].  "Sou" sounds like the SOU of the English word soup, "bre" sounds like a B + the beginning of the word reverse, "saut" sounds like the English word so but with rounded lips (similar to the word sew but without the final W).

Soubresaut is the action of performing a spring into the air from 5th position and landing in the same 5th position, without changing the feet.  The legs cling together in fifth position in the air.  Imagine that you are standing on top of a spring.  You plié and then shoot into the air, coming back down gently on top of the spring.

A spring from fifth position without a change of feet is commonly agreed upon as a soubresaut, but there is disagreement about the necessity for this movement to travel.  In its simplest form the soubresaut is considered to go up and down on top of itself, landing in the dancer's own footprints.  In some schools of thought, the soubresaut always springs forward, carrying the dancer with straight body and tightly held legs en avant.  Still other schools define the soubresaut as traveling in any direction.  What do you think?  Does the soubresaut have to travel?