Gap

Forex trades continuously through the week, so intraday gaps are rare, but the weekend break produces them regularly: news between the Friday close and the Sunday open is expressed as a jump in price rather than a movement through it.

Gaps are the reason a stop loss is a risk-control tool rather than a guarantee. If price opens beyond your stop, the order triggers and fills at the new market price, which may be materially worse than the level you chose.