To understand the spread concept, you first need to distinguish between Ask and Bid prices for each pair.
When making a purchase with a market order, meaning you place a Long order on a pair, your order will be executed at the Ask price. When you want to close the trade, it will be executed at the Bid price. If you place a Sell order, it works in the opposite way - Sell (short) is executed at the Bid price, and closing is executed at the Ask price.
The difference between Ask and Bid prices is called the Spread.
Spreads constantly fluctuate in the market and tend to increase during market instability or low liquidity periods. Conversely, spreads decrease when market liquidity is high.
News events, market rollovers, and political instability create market volatility, affect liquidity, and are factors that increase spreads.
Understanding spread widening is a crucial aspect of trading, and every trader should know how to manage their trades during low liquidity periods. Spread widening can cause slippage, so there's no guarantee that a Stop-Loss will be executed at the desired price level.