This is always so weird to respond to when asked unless it is someone much like me, then it is easy. I feel like I should keep it to myself but since it is you I will attempt an answer, in my own words.
It's just hard to explain when I separate it out like this. I can better explain what it is not. It is not attached to my physical senses in a way that I can articulate but it has to be since I am not a disembodied consciousness. It is not a thought, emotion, feeling or any external pattern recognition, although I have plenty of those too. It is not inner peace or even "harmony" but I have experienced both at times. It arises from within me and even though it sounds weird to others, I just know things that I don't know that I know until I say it. In a socionics sense, I also know most probable outcomes of many situations but I don't like how some socionists almost exclusively associate it with time in the way they do. I think a lot of people can come to the most probable outcomes by using analysis as well. I can do that too. There is a sense of timelessness to my existence especially when I am left to my own devices. I guess that makes sense because time is nothing but a man made construct.
This was all more frustrating and weird as a child, btw. Inside of me are whole other worlds, layered dimensions of experience that I can pull from that seem to come from elsewhere. When someone asks me to describe it I often lose my words, yet other times they can pour out of me in the right setting. Sometimes they feel like they aren't mine but I know they are mine. There are some things that can't even be translated into words.
You know that feeling when some people look at you in awe, fear, or sometimes like you are a lunatic (but they still want to hear it)? I have experienced that a lot irl. I don't think my personality comes across right online to most people even though I get typed an Ni a lot. I would say those who talk to me often, one on one, probably have a better idea of me than what comes out in my posts. I often wonder why they type me that. I think it is for different reasons than I type myself what I do since they have no idea what I am really like. I know why I chose my self type since in Jung's descriptions it is the closest to describing me. Sorry I can't be more help. lol