What does it mean when you see somebody's spirit but there not dead?

Answer 1

Apparitions are classically categorized in four groups, Experimental, Crisis, Post-Mortem and Haunting.

The Experiemental and Crisis apparitions are apparitions of living persons. They are produced either intentionally or spontaneously and seem to involve altered states of concsciousness often called 'out of body' experiences. In both cases, the person producing the apparition directly targets a living individual to whom they will appear, usually as themselves.

It is a common myth that only apparitions of the dead exist. In fact, it is more likely that most apparitions have their origins in living apparitional agents.

Answer 2

Someone is astral projecting...

This could be an Out of Body Experience [OBE].

You can check out multiple websites/books on OBEs.

It means that person wants to tell you a message or spy on you.