The act of doing it is described as "tearing a hole" in the Pattern, but we've never SEEN it from another characters perspective since TEoTW's Prologue. This is the only time we EVER SEE someone entering a place by traveling with the True Power, and also again when he Travels to the island, later known as Tar Valon, at the end of the chapter. Those are the only times. RJ stated that this is what it looks like when you Travel using the True Power. That's what it is.