It’s basically a thoughtform, sometimes called a servitor, that is created by and fed by multiple people. When they get big enough, and if you’ve created them well and choose to free them, they can become independent immortal spirits in their own right.
For example, the thoughtform for this forum is called Mr. Silvera and acts to help ward and protect the members using this forum from external psychic attacks. He used to warn the last Global Mod, who named him and put the work into him, of trouble. The more people work with him, the stronger he will get.