Dragon Soul

A  is the soul of a dragon. They are used to activate words of Dragon Shouts, and with, they can be used to regain perks from perk trees, enabling them to be spent on different skills.

Although words of the dragon language can be learned from word walls without dragon souls, dragon souls are required to unlock them.

Dragon souls are absorbed by the Dragonborn immediately after slaying a Dragon.

In the quest line of Dragonborn, Miraak can steal dragon souls and prevent the Dragonborn from absorbing them.

Use
The number of absorbed dragon souls can be found in the magic tab of the character menu in the bottom-right-hand corner. They are kept until they are spent unlocking a word of a Thu'um. All shouting words other than the ones given to the Dragonborn in the main storyline must be unlocked before they can be used. To do so, acquire a dragon soul, select the word in the magic tab, and press the respective unlock key.

After Miraak is defeated, all the perks in a skill tree can be removed to be used elsewhere at the cost of one dragon soul. This can be done at anytime provided dragon souls are available.

Trivia

 * The souls of Durnehviir, Odahviing, Alduin and dragons at Apocrypha are impossible to be absorbed by the Dragonborn.
 * If the Dragonborn is not near a dragon when it dies, they may not be able to absorb the soul.
 * However, they can come back days later in-game to absorb the dead dragon's soul.
 * Killing Miraak causes his body to burn up like a dragon's, which releases ten souls, as well as any he had stolen from the Dragonborn.
 * Assuming that a dead dragon's soul has yet to be absorbed, the body will remain unburnt. (All dragons that have their souls absorbed remain as bones)

Bugs

 * If the Disintegrate perk is active, using a shock spell may result in the dragon turning into ash and never giving a soul. To fix this, ready both hands as if for a fistfight, and the soul will be absorbed. Confirmed on 360.
 * If a dragon's corpse falls into water, Miraak cannot absorb the soul.
 * A slain dragon may not burn away, thus preventing the acquisition of its soul.
 * May not be able to obtain dragon soul if dragon is killed while in werewolf form.

Drachenseele Alma de Dragón Dragon Soul