Flame and the Void
A similar entry appears in the Wheel of Time Companion confirming the information available in the main story arc.
The flame and the void is a concentration technique, in which someone imagines a flame and then imagines pushing all emotion into it for them to be burned away. For men who can channel, when they are in this state, they are able to sense saidin (TDR, Ch. 7).
I imagine a flame, and then I push everything into it. Hate, fear, nervousness. Everything. When they’re all consumed, there’s an emptiness, a void, inside my head. I am in the middle of it, but I’m a part of whatever I am concentrating on, too.” (Rand, to Elayne and Egwene, The Dragon Reborn, Chapter 7)
The Oneness," she said, sounding satisfied. She saw his questioning look and added, "That is what it is called . . . in some places. The Oneness. To learn the full use of it, it is best to wrap it around you continuously, to dwell in it at all times, or so I've heard." (Lanfear, The Great Hunt, Chapter 16).