A simulation of how a strategy would have performed on past price data.
A backtest runs a strategy's rules over historical prices to estimate what it would have done. It is useful for finding obvious flaws before any money is risked.
A backtest is not a track record. It uses ideal conditions, with no slippage and often with optimistic spreads, and the rules may have been adjusted until the past looked good. Results on a live account are usually worse.
Educational content only, not financial advice. Trading forex involves substantial risk of loss.