The medieval music organ at saint Michel abbey in northern France

The fermata corresponds to the length of time a note is held, the duration of which may be extended at will.

The organ is an instrument which is organised and is composed of several divisions contained in the organ chest. The classification is as follows:

The Great Organ or principal division which groups the most numerous and powerful stops,
The Choir Organ, which has ranks identical to the Great Organ, though finer, and lighter,
The Swell Organ, or Recit which lets the solo stops sing (cornet, oboe, trumpet),
The Echo which responds to the Swell.

Generally the keyboards, have 48 notes of the same tone. The stops may be simple and played solo like the bourdon or flute. They may be composed of a cornet, of a mixture, or of a cymbal, which participates, in these compound sounds.
The range of sounds of an organ is immense in its variety. This is why the acoustic boards are judicially placed in the body of the instrument to give a balanced and harmonious sound. This is the work of the organ builder who gives to each instrument its character, taking into account the hall or church where it will be placed.