Spread is the difference between the bid price and the ask price in any quotation. For example, the (EUR/USD) is quoted at 1.38758/778, and the spread is 2.0 points. Under normal circumstances, the most liquid currency pairs (major currency pairs) have the smallest spreads, and the less liquid currency pairs have larger spreads.
In forex market transactions, there are generally two quotations, the lower is the buyer's price (used when selling short), and the higher is the seller's price (used when buying). Since it is a matchmaking transaction, it is necessary to look at the quotations provided by other traders when trading, so there will be price inconsistencies, and the difference between the two prices is the usual spread.