Star Trek: Every Vulcan Ability You Need To Know

Vulcans don't fear death, they accept it as the logical and inevitable conclusion of life, but sometimes, before a Vulcan dies, they use a mind meld to transfer their life-essence into someone else's brain.

As mentioned earlier, a katra is basically a Vulcan soul. The complete personality and memories of an individual. Transferring their katra into someone else's brain could, in a way, allow Vulcans to live forever. As we saw in the Star Trek: Enterprise episode, The Forge, a Vulcan's katra could even be stored in an inanimate object, a so-called katric ark. Surak, the famous Vulcan philosopher, used a katric ark to preserve his soul for centuries before it was discovered and put into a living host.

Another example of this being used is in Star Trek III: The Search For Spock. Spock transferred his katra into Dr. McCoy shortly before he died, allowing the doctor to revive him by giving the katra to a newly created clone of Spock.