Shared dreams are a very unique and strange phenomenon that is defined as being experienced by two or more people. The dreamers are not witnessing the exact same dream, but are experiencing the same dream scape from two different viewpoint. No different than how two individuals meeting in waking life will have two different views on an event the experience together, like walking down a street.
A normal dream may include a representation of a person you know in waking life without that person actually being present in the dream. A shared dream however has the persons full, often lucid, consciousness existing alongside your own. Shared dreams can take on any number of forms from nonsensical to incredibly logical "realistic" forms the same as a normal dream. They can also go a step further into what I call a Projection Dream or Full Transition. A state where your body is sleeping but your consciousness has fully transferred over to your "dream body". Such states are completely indistinguishable from normal waking reality unless something really nonsensical occurs during that state, such as a penguin talking to you about flower arranging.
There appears to be some form of prerequisites before a person can share a dream with another. One major one seems to be a past life connection with the person or equivalent closeness such as lifelong friendships. Another appears to be a certain degree of competence in manipulating energy, aka "magic" as such skills necessarily strengthen your energy "muscle". This increase in available energy seems to be needed to connect the two dreamers.
As an example, Reikara and I have been having shared dreams with each other before we even knew each other existed. We've been able to confirm this on dozens of occasions by telling each other portions of dreams we suspected we might've shared, seeing if the other person can fill in the information we're withholding. The test is set up in such a way that the other person cannot possibly have any other way of knowing the information except if they were also present during the event. This guards against us constructing false memories after hearing the full dream and thus only being able to respond "Oh yes I knew that". Because anyone could say that and thus it proves nothing. The key is being able to provide details that were not stated but were experienced by both parties.
Sure its not a perfect system but its been working well for us. It's allowed us to call out douchebaggy fakes who just want people to tell them how special they are as well which is a nice perk. But really anyone can use this method dishonestly, its not that hard. For example lets say you want someone to prove they saw you, so you ask them some relatively vague question about something prominent about your appearance like “what colour were my eyes?” which on the surface sounds like a BS question until you realize that your are not constrained to 'normal' eye colours, and is especially good to use if one day your eye colour was radically different than it normally is. Now, lets say they answer right, and its a colour like deep lavender purple with gray streaks or something. You tell them they're right, and they are right, but what proof do they actually have that you didn't just agree with what they said? They could've said anything at all and you could say they were right without them really knowing if you're lying or not. So yes there's a danger to it, even if they then go on to give extra details that you never asked for (as is common with us) you could still just agree with them.
But there is one caveat to this that seems very foolproof. It is said that one should never lie unless they have a very good memory. Sure you may not manage to catch them right away if they lied, but it is commonplace for us to also test the person for contradictions. And when we find them, we know it was jut a lie. This method is also how we confirmed our past life connections to each other as our respective stories that we attempted to write before learning they were memories overlapped at one point. Something we were able to definitively prove because we were able to provide details that were impossible for us to know otherwise.
Interestingly enough too, you can project yourself into another persons dreams even though you yourself are not sleeping. For Reikara and I this is the most common means of us sharing dreams because she is on the other side of the world. This brings up important questions about what projection (astral, spirit, consciousness, OOBE, etc, whatever you wanna call it) actually is.
In addition to this there appears to be an interesting time delay phenomenon that occurs sometimes. One person will have their side of the dream sometimes years apart from when the other person has theirs. Example, Reikara's first confirmed shared experience with me happened in 2004, and she knows this for a fact because after she woke up from that dream she drew a picture of a large flaming phoenix that accosted us in there. I on the other hand had my part of this in 2010, and that phoenix was actually a friend of mine, Jeremy Greene, who was being a dick at the time. He had used some magic to transform either Velagneur or himself (I don't remember right now but probably Velagneur) into that phoenix to do mock charges at us so that would freak out not realizing there was no danger and leap into my arms gong “Oh save me, save me knight in shining armor!” because she was a noob at the whole projection thing..... and because he's a douchebag like that. I had a few words with him about it after. >_>
Since that event the delay between our experiences has shortened from years to months to weeks to days to now basically being realtime. We don't actually know why this is but I personally suspect it to be somehow influenced by a dimensional barrier we call the Distortion Field because it appears to have some temporal properties to it. Not to be confused with another barrier we call the Veil which is a planar barrier, not a dimensional one. More on what I think that all is later.
I hope I did a good job explaining all this and if I haven't please ask me questions as I will be more than happy to explain things. I especially hope I get questions from people who are not well versed in the world of the paranormal as my goal is to demystify these misunderstood realm of reality.