4 Stroking definition help

[Scrat]

Could you guys clearly define "4 stroking" in regard to tuning. The term is not clear to me. I just did an exhaust modification to a Husqvarna 334T and adjusted the carb. The Tach says it is running at 13,600 with great throttle response and very smooth at that RPM, no lugging or any issues even with the bar fully burried in a piece of Red Oak. I am posting it in this area because I would like a professional answer. Thanks in advance for your responses