From D&D Wiki
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A creature with this ability can communicate telepathically with any other creature within a certain range (specified in the creature’s entry, usually 100 feet) that has a language. It is possible to address multiple creatures at once telepathically, although maintaining a telepathic conversation with more than one creature at a time is just as difficult as simultaneously speaking and listening to multiple people at the same time.
Some creatures have a limited form of telepathy, while others have a more powerful form of the ability.