For 6 panel caps, that means there are 6 panels on the crown of the cap.
https://everlight-trade.com/product/3d-embroidery-baseball-cap-tye-dye/
6 panel caps
You can see the above cap, there is a seam in the middle of the front.
Compare with the 5 panel caps, the 6-panel cap has two front panels, this gives a rounded appearance in the front.
This allows 6 panel cap suits for more styles, from classic to modern, from Snapback cap to Dad cap.
Another difference with 5 panel caps, the logo could not be printed on the front of 6 panel caps. Because there is a seam, but very suitable for embroidery.