The dressage judge is looking for an overall pleasing picture of a partnership between horse and rider. The picture should also be of good balance, self carriage and cadence. A fair amount of straightness is required and an easy bend. The paces should be unrestricted allowing a looseness through the back and neck, and the poll must be the highest point so that some weight can be carried on the hind legs.
The judge will look for the same, but with a little more of everything. The horse should be straighter and maintain his balance and cadence through the more difficult circles and transitions.. He must be honest to the riders aids.
More of the same is required with the horse staying honest to the aids, moving off the leg exactly when asked without delay. The improved balance ensures the hind legs are taking more weight and the forehand is becoming lighter. If the movements look easy and harmonious, the poll is still the highest point and the horse is travelling willingly in an uphill balance then you know that the collection is enough for the level of test you are riding.
The word COLLECTION is really the combination of balance, self carriage, cadence and rhythm, and straightness.