Psychoprojective telepathy
Psychoprojective telepathy was a telepathic ability of the Halanans. It apparently entailed projecting a seemingly solid image of ones' self, which could act out subconscious personality traits.

On a visit to Deep Space 9 aboard the  in 2370, Nidell lost control of her psychoprojective telepathy, allowing Fenna to appear to Benjamin Sisko. ()

See also 

 Mental Projection at Wikipedia
Astral Projection at Wikipedia

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Physiology
Psychology