Round-Trip Cost
The total cost of entering and exiting a position: the exchange's fee on both sides plus the slippage between the intended and achieved price.
Ignoring it makes every statistic slightly wrong and some of them completely wrong. A target three percent away survives a fifth of a percent in costs comfortably; a target a tenth of a percent away is erased by it, and a strategy built on such targets can show a high hit rate while losing money on every trade. This site charges a fifth of a percent against both sides of every backtested trade — a taker fee near the top of the retail band plus slippage of similar size — deliberately chosen so the published figures do not depend on having a favourable fee schedule.